diff --git a/UPGRADE-4.0.md b/UPGRADE-4.0.md
index f94259329e5a0..812d2ba5e90fd 100644
--- a/UPGRADE-4.0.md
+++ b/UPGRADE-4.0.md
@@ -146,7 +146,7 @@ DependencyInjection
    <service id="Doctrine\Common\Annotations\Reader" alias="annotations.reader" public="false" />
    ```
 
- * Service identifiers are now case sensitive.
+ * Service identifiers and parameter names are now case sensitive.
 
  * The `Reference` and `Alias` classes do not make service identifiers lowercase anymore.
 
diff --git a/src/Symfony/Component/DependencyInjection/CHANGELOG.md b/src/Symfony/Component/DependencyInjection/CHANGELOG.md
index 1e51a5c927f29..26df6aa372f7f 100644
--- a/src/Symfony/Component/DependencyInjection/CHANGELOG.md
+++ b/src/Symfony/Component/DependencyInjection/CHANGELOG.md
@@ -21,6 +21,7 @@ CHANGELOG
  * removed silent behavior for unused attributes and elements
  * removed support for setting and accessing private services in `Container`
  * removed support for setting pre-defined services in `Container`
+ * removed support for case insensitivity of parameter names
 
 3.4.0
 -----
diff --git a/src/Symfony/Component/DependencyInjection/Dumper/PhpDumper.php b/src/Symfony/Component/DependencyInjection/Dumper/PhpDumper.php
index 93a0ccda3eeba..0c955341a46e8 100644
--- a/src/Symfony/Component/DependencyInjection/Dumper/PhpDumper.php
+++ b/src/Symfony/Component/DependencyInjection/Dumper/PhpDumper.php
@@ -1039,15 +1039,11 @@ private function addDefaultParametersMethod()
 
         $php = array();
         $dynamicPhp = array();
-        $normalizedParams = array();
 
         foreach ($this->container->getParameterBag()->all() as $key => $value) {
             if ($key !== $resolvedKey = $this->container->resolveEnvPlaceholders($key)) {
                 throw new InvalidArgumentException(sprintf('Parameter name cannot use env parameters: %s.', $resolvedKey));
             }
-            if ($key !== $lcKey = strtolower($key)) {
-                $normalizedParams[] = sprintf('        %s => %s,', $this->export($lcKey), $this->export($key));
-            }
             $export = $this->exportParameters(array($value));
             $export = explode('0 => ', substr(rtrim($export, " )\n"), 7, -1), 2);
 
@@ -1066,12 +1062,10 @@ private function addDefaultParametersMethod()
      */
     public function getParameter($name)
     {
-        if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
-            $name = $this->normalizeParameterName($name);
+        $name = (string) $name;
 
-            if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
-                throw new InvalidArgumentException(sprintf('The parameter "%s" must be defined.', $name));
-            }
+        if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
+            throw new InvalidArgumentException(sprintf('The parameter "%s" must be defined.', $name));
         }
         if (isset($this->loadedDynamicParameters[$name])) {
             return $this->loadedDynamicParameters[$name] ? $this->dynamicParameters[$name] : $this->getDynamicParameter($name);
@@ -1085,7 +1079,7 @@ public function getParameter($name)
      */
     public function hasParameter($name)
     {
-        $name = $this->normalizeParameterName($name);
+        $name = (string) $name;
 
         return isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters);
     }
@@ -1155,30 +1149,6 @@ private function getDynamicParameter(\$name)
 {$getDynamicParameter}
     }
 
-
-EOF;
-
-        $code .= '    private $normalizedParameterNames = '.($normalizedParams ? sprintf("array(\n%s\n    );", implode("\n", $normalizedParams)) : 'array();')."\n";
-        $code .= <<<'EOF'
-
-    private function normalizeParameterName($name)
-    {
-        if (isset($this->normalizedParameterNames[$normalizedName = strtolower($name)]) || isset($this->parameters[$normalizedName]) || array_key_exists($normalizedName, $this->parameters)) {
-            $normalizedName = isset($this->normalizedParameterNames[$normalizedName]) ? $this->normalizedParameterNames[$normalizedName] : $normalizedName;
-            if ((string) $name !== $normalizedName) {
-                @trigger_error(sprintf('Parameter names will be made case sensitive in Symfony 4.0. Using "%s" instead of "%s" is deprecated since version 3.4.', $name, $normalizedName), E_USER_DEPRECATED);
-            }
-        } else {
-            $normalizedName = $this->normalizedParameterNames[$normalizedName] = (string) $name;
-        }
-
-        return $normalizedName;
-    }
-
-EOF;
-
-        $code .= <<<EOF
-
     /*{$this->docStar}
      * Gets the default parameters.
      *
@@ -1643,7 +1613,7 @@ private function getServiceCall($id, Reference $reference = null)
         if ('service_container' === $id) {
             return '$this';
         }
-        
+
         if ($this->container->hasDefinition($id)) {
             $definition = $this->container->getDefinition($id);
 
diff --git a/src/Symfony/Component/DependencyInjection/ParameterBag/ParameterBag.php b/src/Symfony/Component/DependencyInjection/ParameterBag/ParameterBag.php
index 1a9ca6fa4d4fb..d623428ef2abb 100644
--- a/src/Symfony/Component/DependencyInjection/ParameterBag/ParameterBag.php
+++ b/src/Symfony/Component/DependencyInjection/ParameterBag/ParameterBag.php
@@ -25,8 +25,6 @@ class ParameterBag implements ParameterBagInterface
     protected $parameters = array();
     protected $resolved = false;
 
-    private $normalizedNames = array();
-
     /**
      * @param array $parameters An array of parameters
      */
@@ -68,7 +66,7 @@ public function all()
      */
     public function get($name)
     {
-        $name = $this->normalizeName($name);
+        $name = (string) $name;
 
         if (!array_key_exists($name, $this->parameters)) {
             if (!$name) {
@@ -113,7 +111,7 @@ public function get($name)
      */
     public function set($name, $value)
     {
-        $this->parameters[$this->normalizeName($name)] = $value;
+        $this->parameters[(string) $name] = $value;
     }
 
     /**
@@ -121,7 +119,7 @@ public function set($name, $value)
      */
     public function has($name)
     {
-        return array_key_exists($this->normalizeName($name), $this->parameters);
+        return array_key_exists((string) $name, $this->parameters);
     }
 
     /**
@@ -131,7 +129,7 @@ public function has($name)
      */
     public function remove($name)
     {
-        unset($this->parameters[$this->normalizeName($name)]);
+        unset($this->parameters[(string) $name]);
     }
 
     /**
@@ -208,13 +206,12 @@ public function resolveString($value, array $resolving = array())
         // a non-string in a parameter value
         if (preg_match('/^%([^%\s]+)%$/', $value, $match)) {
             $key = $match[1];
-            $lcKey = strtolower($key); // strtolower() to be removed in 4.0
 
-            if (isset($resolving[$lcKey])) {
+            if (isset($resolving[$key])) {
                 throw new ParameterCircularReferenceException(array_keys($resolving));
             }
 
-            $resolving[$lcKey] = true;
+            $resolving[$key] = true;
 
             return $this->resolved ? $this->get($key) : $this->resolveValue($this->get($key), $resolving);
         }
@@ -226,8 +223,7 @@ public function resolveString($value, array $resolving = array())
             }
 
             $key = $match[1];
-            $lcKey = strtolower($key); // strtolower() to be removed in 4.0
-            if (isset($resolving[$lcKey])) {
+            if (isset($resolving[$key])) {
                 throw new ParameterCircularReferenceException(array_keys($resolving));
             }
 
@@ -238,7 +234,7 @@ public function resolveString($value, array $resolving = array())
             }
 
             $resolved = (string) $resolved;
-            $resolving[$lcKey] = true;
+            $resolving[$key] = true;
 
             return $this->isResolved() ? $resolved : $this->resolveString($resolved, $resolving);
         }, $value);
@@ -290,18 +286,4 @@ public function unescapeValue($value)
 
         return $value;
     }
-
-    private function normalizeName($name)
-    {
-        if (isset($this->normalizedNames[$normalizedName = strtolower($name)])) {
-            $normalizedName = $this->normalizedNames[$normalizedName];
-            if ((string) $name !== $normalizedName) {
-                @trigger_error(sprintf('Parameter names will be made case sensitive in Symfony 4.0. Using "%s" instead of "%s" is deprecated since version 3.4.', $name, $normalizedName), E_USER_DEPRECATED);
-            }
-        } else {
-            $normalizedName = $this->normalizedNames[$normalizedName] = (string) $name;
-        }
-
-        return $normalizedName;
-    }
 }
diff --git a/src/Symfony/Component/DependencyInjection/Tests/ContainerBuilderTest.php b/src/Symfony/Component/DependencyInjection/Tests/ContainerBuilderTest.php
index d48c2460dc2fc..ba8e28cec3711 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/ContainerBuilderTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/ContainerBuilderTest.php
@@ -1098,19 +1098,15 @@ public function testCaseSensitivity()
         $this->assertSame($container->get('fOO')->Foo->foo, $container->get('foo'), '->get() returns the service for the given id, case sensitively');
     }
 
-    /**
-     * @group legacy
-     * @expectedDeprecation Parameter names will be made case sensitive in Symfony 4.0. Using "FOO" instead of "foo" is deprecated since version 3.4.
-     */
     public function testParameterWithMixedCase()
     {
-        $container = new ContainerBuilder(new ParameterBag(array('foo' => 'bar')));
+        $container = new ContainerBuilder(new ParameterBag(array('foo' => 'bar', 'FOO' => 'BAR')));
         $container->register('foo', 'stdClass')
             ->setProperty('foo', '%FOO%');
 
         $container->compile();
 
-        $this->assertSame('bar', $container->get('foo')->foo);
+        $this->assertSame('BAR', $container->get('foo')->foo);
     }
 }
 
diff --git a/src/Symfony/Component/DependencyInjection/Tests/ContainerTest.php b/src/Symfony/Component/DependencyInjection/Tests/ContainerTest.php
index 30eefb5546d72..513dff8450779 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/ContainerTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/ContainerTest.php
@@ -121,18 +121,13 @@ public function testGetSetParameter()
         }
     }
 
-    /**
-     * @group legacy
-     * @expectedDeprecation Parameter names will be made case sensitive in Symfony 4.0. Using "Foo" instead of "foo" is deprecated since version 3.4.
-     * @expectedDeprecation Parameter names will be made case sensitive in Symfony 4.0. Using "FOO" instead of "foo" is deprecated since version 3.4.
-     */
     public function testGetSetParameterWithMixedCase()
     {
         $sc = new Container(new ParameterBag(array('foo' => 'bar')));
 
         $sc->setParameter('Foo', 'baz1');
-        $this->assertEquals('baz1', $sc->getParameter('foo'), '->setParameter() converts the key to lowercase');
-        $this->assertEquals('baz1', $sc->getParameter('FOO'), '->getParameter() converts the key to lowercase');
+        $this->assertEquals('bar', $sc->getParameter('foo'));
+        $this->assertEquals('baz1', $sc->getParameter('Foo'));
     }
 
     public function testGetServiceIds()
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Dumper/PhpDumperTest.php b/src/Symfony/Component/DependencyInjection/Tests/Dumper/PhpDumperTest.php
index 47356e2d5c8a8..af60d67ca23e8 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Dumper/PhpDumperTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Dumper/PhpDumperTest.php
@@ -651,12 +651,6 @@ public function testPrivateServiceTriggersDeprecation()
         $container->get('bar');
     }
 
-    /**
-     * @group legacy
-     * @expectedDeprecation Parameter names will be made case sensitive in Symfony 4.0. Using "foo" instead of "Foo" is deprecated since version 3.4.
-     * @expectedDeprecation Parameter names will be made case sensitive in Symfony 4.0. Using "FOO" instead of "Foo" is deprecated since version 3.4.
-     * @expectedDeprecation Parameter names will be made case sensitive in Symfony 4.0. Using "bar" instead of "BAR" is deprecated since version 3.4.
-     */
     public function testParameterWithMixedCase()
     {
         $container = new ContainerBuilder(new ParameterBag(array('Foo' => 'bar', 'BAR' => 'foo')));
@@ -667,26 +661,7 @@ public function testParameterWithMixedCase()
 
         $container = new \Symfony_DI_PhpDumper_Test_Parameter_With_Mixed_Case();
 
-        $this->assertSame('bar', $container->getParameter('foo'));
-        $this->assertSame('bar', $container->getParameter('FOO'));
-        $this->assertSame('foo', $container->getParameter('bar'));
+        $this->assertSame('bar', $container->getParameter('Foo'));
         $this->assertSame('foo', $container->getParameter('BAR'));
     }
-
-    /**
-     * @group legacy
-     * @expectedDeprecation Parameter names will be made case sensitive in Symfony 4.0. Using "FOO" instead of "foo" is deprecated since version 3.4.
-     */
-    public function testParameterWithLowerCase()
-    {
-        $container = new ContainerBuilder(new ParameterBag(array('foo' => 'bar')));
-        $container->compile();
-
-        $dumper = new PhpDumper($container);
-        eval('?>'.$dumper->dump(array('class' => 'Symfony_DI_PhpDumper_Test_Parameter_With_Lower_Case')));
-
-        $container = new \Symfony_DI_PhpDumper_Test_Parameter_With_Lower_Case();
-
-        $this->assertSame('bar', $container->getParameter('FOO'));
-    }
 }
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services10.php b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services10.php
index 582472b38bd7a..d914e82378567 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services10.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services10.php
@@ -77,12 +77,10 @@ protected function getTestService()
      */
     public function getParameter($name)
     {
-        if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
-            $name = $this->normalizeParameterName($name);
+        $name = (string) $name;
 
-            if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
-                throw new InvalidArgumentException(sprintf('The parameter "%s" must be defined.', $name));
-            }
+        if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
+            throw new InvalidArgumentException(sprintf('The parameter "%s" must be defined.', $name));
         }
         if (isset($this->loadedDynamicParameters[$name])) {
             return $this->loadedDynamicParameters[$name] ? $this->dynamicParameters[$name] : $this->getDynamicParameter($name);
@@ -96,7 +94,7 @@ public function getParameter($name)
      */
     public function hasParameter($name)
     {
-        $name = $this->normalizeParameterName($name);
+        $name = (string) $name;
 
         return isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters);
     }
@@ -142,22 +140,6 @@ private function getDynamicParameter($name)
         throw new InvalidArgumentException(sprintf('The dynamic parameter "%s" must be defined.', $name));
     }
 
-    private $normalizedParameterNames = array();
-
-    private function normalizeParameterName($name)
-    {
-        if (isset($this->normalizedParameterNames[$normalizedName = strtolower($name)]) || isset($this->parameters[$normalizedName]) || array_key_exists($normalizedName, $this->parameters)) {
-            $normalizedName = isset($this->normalizedParameterNames[$normalizedName]) ? $this->normalizedParameterNames[$normalizedName] : $normalizedName;
-            if ((string) $name !== $normalizedName) {
-                @trigger_error(sprintf('Parameter names will be made case sensitive in Symfony 4.0. Using "%s" instead of "%s" is deprecated since version 3.4.', $name, $normalizedName), E_USER_DEPRECATED);
-            }
-        } else {
-            $normalizedName = $this->normalizedParameterNames[$normalizedName] = (string) $name;
-        }
-
-        return $normalizedName;
-    }
-
     /**
      * Gets the default parameters.
      *
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services12.php b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services12.php
index f5db7d75d4b43..6df51ea0899bb 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services12.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services12.php
@@ -81,12 +81,10 @@ protected function getTestService()
      */
     public function getParameter($name)
     {
-        if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
-            $name = $this->normalizeParameterName($name);
+        $name = (string) $name;
 
-            if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
-                throw new InvalidArgumentException(sprintf('The parameter "%s" must be defined.', $name));
-            }
+        if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
+            throw new InvalidArgumentException(sprintf('The parameter "%s" must be defined.', $name));
         }
         if (isset($this->loadedDynamicParameters[$name])) {
             return $this->loadedDynamicParameters[$name] ? $this->dynamicParameters[$name] : $this->getDynamicParameter($name);
@@ -100,7 +98,7 @@ public function getParameter($name)
      */
     public function hasParameter($name)
     {
-        $name = $this->normalizeParameterName($name);
+        $name = (string) $name;
 
         return isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters);
     }
@@ -156,22 +154,6 @@ private function getDynamicParameter($name)
         return $this->dynamicParameters[$name] = $value;
     }
 
-    private $normalizedParameterNames = array();
-
-    private function normalizeParameterName($name)
-    {
-        if (isset($this->normalizedParameterNames[$normalizedName = strtolower($name)]) || isset($this->parameters[$normalizedName]) || array_key_exists($normalizedName, $this->parameters)) {
-            $normalizedName = isset($this->normalizedParameterNames[$normalizedName]) ? $this->normalizedParameterNames[$normalizedName] : $normalizedName;
-            if ((string) $name !== $normalizedName) {
-                @trigger_error(sprintf('Parameter names will be made case sensitive in Symfony 4.0. Using "%s" instead of "%s" is deprecated since version 3.4.', $name, $normalizedName), E_USER_DEPRECATED);
-            }
-        } else {
-            $normalizedName = $this->normalizedParameterNames[$normalizedName] = (string) $name;
-        }
-
-        return $normalizedName;
-    }
-
     /**
      * Gets the default parameters.
      *
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services26.php b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services26.php
index f7eb32e55e75f..5d5978f1fcf45 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services26.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services26.php
@@ -79,12 +79,10 @@ protected function getTestService()
      */
     public function getParameter($name)
     {
-        if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
-            $name = $this->normalizeParameterName($name);
+        $name = (string) $name;
 
-            if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
-                throw new InvalidArgumentException(sprintf('The parameter "%s" must be defined.', $name));
-            }
+        if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
+            throw new InvalidArgumentException(sprintf('The parameter "%s" must be defined.', $name));
         }
         if (isset($this->loadedDynamicParameters[$name])) {
             return $this->loadedDynamicParameters[$name] ? $this->dynamicParameters[$name] : $this->getDynamicParameter($name);
@@ -98,7 +96,7 @@ public function getParameter($name)
      */
     public function hasParameter($name)
     {
-        $name = $this->normalizeParameterName($name);
+        $name = (string) $name;
 
         return isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters);
     }
@@ -152,24 +150,6 @@ private function getDynamicParameter($name)
         return $this->dynamicParameters[$name] = $value;
     }
 
-    private $normalizedParameterNames = array(
-        'env(foo)' => 'env(FOO)',
-    );
-
-    private function normalizeParameterName($name)
-    {
-        if (isset($this->normalizedParameterNames[$normalizedName = strtolower($name)]) || isset($this->parameters[$normalizedName]) || array_key_exists($normalizedName, $this->parameters)) {
-            $normalizedName = isset($this->normalizedParameterNames[$normalizedName]) ? $this->normalizedParameterNames[$normalizedName] : $normalizedName;
-            if ((string) $name !== $normalizedName) {
-                @trigger_error(sprintf('Parameter names will be made case sensitive in Symfony 4.0. Using "%s" instead of "%s" is deprecated since version 3.4.', $name, $normalizedName), E_USER_DEPRECATED);
-            }
-        } else {
-            $normalizedName = $this->normalizedParameterNames[$normalizedName] = (string) $name;
-        }
-
-        return $normalizedName;
-    }
-
     /**
      * Gets the default parameters.
      *
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services8.php b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services8.php
index bbd0b34c58f3c..0344b03935341 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services8.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services8.php
@@ -64,12 +64,10 @@ public function isCompiled()
      */
     public function getParameter($name)
     {
-        if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
-            $name = $this->normalizeParameterName($name);
+        $name = (string) $name;
 
-            if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
-                throw new InvalidArgumentException(sprintf('The parameter "%s" must be defined.', $name));
-            }
+        if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
+            throw new InvalidArgumentException(sprintf('The parameter "%s" must be defined.', $name));
         }
         if (isset($this->loadedDynamicParameters[$name])) {
             return $this->loadedDynamicParameters[$name] ? $this->dynamicParameters[$name] : $this->getDynamicParameter($name);
@@ -83,7 +81,7 @@ public function getParameter($name)
      */
     public function hasParameter($name)
     {
-        $name = $this->normalizeParameterName($name);
+        $name = (string) $name;
 
         return isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters);
     }
@@ -129,22 +127,6 @@ private function getDynamicParameter($name)
         throw new InvalidArgumentException(sprintf('The dynamic parameter "%s" must be defined.', $name));
     }
 
-    private $normalizedParameterNames = array();
-
-    private function normalizeParameterName($name)
-    {
-        if (isset($this->normalizedParameterNames[$normalizedName = strtolower($name)]) || isset($this->parameters[$normalizedName]) || array_key_exists($normalizedName, $this->parameters)) {
-            $normalizedName = isset($this->normalizedParameterNames[$normalizedName]) ? $this->normalizedParameterNames[$normalizedName] : $normalizedName;
-            if ((string) $name !== $normalizedName) {
-                @trigger_error(sprintf('Parameter names will be made case sensitive in Symfony 4.0. Using "%s" instead of "%s" is deprecated since version 3.4.', $name, $normalizedName), E_USER_DEPRECATED);
-            }
-        } else {
-            $normalizedName = $this->normalizedParameterNames[$normalizedName] = (string) $name;
-        }
-
-        return $normalizedName;
-    }
-
     /**
      * Gets the default parameters.
      *
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services9_as_files.txt b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services9_as_files.txt
index d5f8d4f65e0a1..66df2f0e0dcfb 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services9_as_files.txt
+++ b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services9_as_files.txt
@@ -382,12 +382,10 @@ class Container%s extends Container
      */
     public function getParameter($name)
     {
-        if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
-            $name = $this->normalizeParameterName($name);
+        $name = (string) $name;
 
-            if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
-                throw new InvalidArgumentException(sprintf('The parameter "%s" must be defined.', $name));
-            }
+        if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
+            throw new InvalidArgumentException(sprintf('The parameter "%s" must be defined.', $name));
         }
         if (isset($this->loadedDynamicParameters[$name])) {
             return $this->loadedDynamicParameters[$name] ? $this->dynamicParameters[$name] : $this->getDynamicParameter($name);
@@ -401,7 +399,7 @@ class Container%s extends Container
      */
     public function hasParameter($name)
     {
-        $name = $this->normalizeParameterName($name);
+        $name = (string) $name;
 
         return isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters);
     }
@@ -447,22 +445,6 @@ class Container%s extends Container
         throw new InvalidArgumentException(sprintf('The dynamic parameter "%s" must be defined.', $name));
     }
 
-    private $normalizedParameterNames = array();
-
-    private function normalizeParameterName($name)
-    {
-        if (isset($this->normalizedParameterNames[$normalizedName = strtolower($name)]) || isset($this->parameters[$normalizedName]) || array_key_exists($normalizedName, $this->parameters)) {
-            $normalizedName = isset($this->normalizedParameterNames[$normalizedName]) ? $this->normalizedParameterNames[$normalizedName] : $normalizedName;
-            if ((string) $name !== $normalizedName) {
-                @trigger_error(sprintf('Parameter names will be made case sensitive in Symfony 4.0. Using "%s" instead of "%s" is deprecated since version 3.4.', $name, $normalizedName), E_USER_DEPRECATED);
-            }
-        } else {
-            $normalizedName = $this->normalizedParameterNames[$normalizedName] = (string) $name;
-        }
-
-        return $normalizedName;
-    }
-
     /**
      * Gets the default parameters.
      *
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services9_compiled.php b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services9_compiled.php
index 30f58e1d974fd..76470376239f3 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services9_compiled.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services9_compiled.php
@@ -391,12 +391,10 @@ protected function getFactorySimpleService()
      */
     public function getParameter($name)
     {
-        if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
-            $name = $this->normalizeParameterName($name);
+        $name = (string) $name;
 
-            if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
-                throw new InvalidArgumentException(sprintf('The parameter "%s" must be defined.', $name));
-            }
+        if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
+            throw new InvalidArgumentException(sprintf('The parameter "%s" must be defined.', $name));
         }
         if (isset($this->loadedDynamicParameters[$name])) {
             return $this->loadedDynamicParameters[$name] ? $this->dynamicParameters[$name] : $this->getDynamicParameter($name);
@@ -410,7 +408,7 @@ public function getParameter($name)
      */
     public function hasParameter($name)
     {
-        $name = $this->normalizeParameterName($name);
+        $name = (string) $name;
 
         return isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters);
     }
@@ -456,22 +454,6 @@ private function getDynamicParameter($name)
         throw new InvalidArgumentException(sprintf('The dynamic parameter "%s" must be defined.', $name));
     }
 
-    private $normalizedParameterNames = array();
-
-    private function normalizeParameterName($name)
-    {
-        if (isset($this->normalizedParameterNames[$normalizedName = strtolower($name)]) || isset($this->parameters[$normalizedName]) || array_key_exists($normalizedName, $this->parameters)) {
-            $normalizedName = isset($this->normalizedParameterNames[$normalizedName]) ? $this->normalizedParameterNames[$normalizedName] : $normalizedName;
-            if ((string) $name !== $normalizedName) {
-                @trigger_error(sprintf('Parameter names will be made case sensitive in Symfony 4.0. Using "%s" instead of "%s" is deprecated since version 3.4.', $name, $normalizedName), E_USER_DEPRECATED);
-            }
-        } else {
-            $normalizedName = $this->normalizedParameterNames[$normalizedName] = (string) $name;
-        }
-
-        return $normalizedName;
-    }
-
     /**
      * Gets the default parameters.
      *
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services_array_params.php b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services_array_params.php
index bf9e7c1dcfffa..ae3da978af978 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services_array_params.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/php/services_array_params.php
@@ -85,12 +85,10 @@ protected function getBarService()
      */
     public function getParameter($name)
     {
-        if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
-            $name = $this->normalizeParameterName($name);
+        $name = (string) $name;
 
-            if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
-                throw new InvalidArgumentException(sprintf('The parameter "%s" must be defined.', $name));
-            }
+        if (!(isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters))) {
+            throw new InvalidArgumentException(sprintf('The parameter "%s" must be defined.', $name));
         }
         if (isset($this->loadedDynamicParameters[$name])) {
             return $this->loadedDynamicParameters[$name] ? $this->dynamicParameters[$name] : $this->getDynamicParameter($name);
@@ -104,7 +102,7 @@ public function getParameter($name)
      */
     public function hasParameter($name)
     {
-        $name = $this->normalizeParameterName($name);
+        $name = (string) $name;
 
         return isset($this->parameters[$name]) || isset($this->loadedDynamicParameters[$name]) || array_key_exists($name, $this->parameters);
     }
@@ -160,22 +158,6 @@ private function getDynamicParameter($name)
         return $this->dynamicParameters[$name] = $value;
     }
 
-    private $normalizedParameterNames = array();
-
-    private function normalizeParameterName($name)
-    {
-        if (isset($this->normalizedParameterNames[$normalizedName = strtolower($name)]) || isset($this->parameters[$normalizedName]) || array_key_exists($normalizedName, $this->parameters)) {
-            $normalizedName = isset($this->normalizedParameterNames[$normalizedName]) ? $this->normalizedParameterNames[$normalizedName] : $normalizedName;
-            if ((string) $name !== $normalizedName) {
-                @trigger_error(sprintf('Parameter names will be made case sensitive in Symfony 4.0. Using "%s" instead of "%s" is deprecated since version 3.4.', $name, $normalizedName), E_USER_DEPRECATED);
-            }
-        } else {
-            $normalizedName = $this->normalizedParameterNames[$normalizedName] = (string) $name;
-        }
-
-        return $normalizedName;
-    }
-
     /**
      * Gets the default parameters.
      *
diff --git a/src/Symfony/Component/DependencyInjection/Tests/ParameterBag/ParameterBagTest.php b/src/Symfony/Component/DependencyInjection/Tests/ParameterBag/ParameterBagTest.php
index 3bac9ca64e20d..c53decf8f017d 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/ParameterBag/ParameterBagTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/ParameterBag/ParameterBagTest.php
@@ -106,28 +106,20 @@ public function testHas()
         $this->assertFalse($bag->has('bar'), '->has() returns false if a parameter is not defined');
     }
 
-    /**
-     * @group legacy
-     * @expectedDeprecation Parameter names will be made case sensitive in Symfony 4.0. Using "BAR" instead of "bar" is deprecated since version 3.4.
-     * @expectedDeprecation Parameter names will be made case sensitive in Symfony 4.0. Using "Foo" instead of "foo" is deprecated since version 3.4.
-     * @expectedDeprecation Parameter names will be made case sensitive in Symfony 4.0. Using "FOO" instead of "foo" is deprecated since version 3.4.
-     * @expectedDeprecation Parameter names will be made case sensitive in Symfony 4.0. Using "Foo" instead of "foo" is deprecated since version 3.4.
-     */
     public function testMixedCase()
     {
         $bag = new ParameterBag(array(
             'foo' => 'foo',
             'bar' => 'bar',
+            'BAR' => 'baz',
         ));
 
         $bag->remove('BAR');
-        $this->assertEquals(array('foo' => 'foo'), $bag->all(), '->remove() converts key to lowercase before removing');
+        $this->assertEquals(array('foo' => 'foo', 'bar' => 'bar'), $bag->all());
 
         $bag->set('Foo', 'baz1');
-        $this->assertEquals('baz1', $bag->get('foo'), '->set() converts the key to lowercase');
-        $this->assertEquals('baz1', $bag->get('FOO'), '->get() converts the key to lowercase');
-
-        $this->assertTrue($bag->has('Foo'), '->has() converts the key to lowercase');
+        $this->assertEquals('foo', $bag->get('foo'));
+        $this->assertEquals('baz1', $bag->get('Foo'));
     }
 
     public function testResolveValue()