diff --git a/doc/api/next_api_changes/deprecations/XXXXX-AL.rst b/doc/api/next_api_changes/deprecations/XXXXX-AL.rst
new file mode 100644
index 000000000000..41a0c09bb22c
--- /dev/null
+++ b/doc/api/next_api_changes/deprecations/XXXXX-AL.rst
@@ -0,0 +1,3 @@
+``RendererAgg.tostring_rgb`` and ``FigureCanvasAgg.tostring_rgb``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+... are deprecated with no replacement.
diff --git a/lib/matplotlib/backends/backend_agg.py b/lib/matplotlib/backends/backend_agg.py
index 47892aacd425..3d7dfa57a82e 100644
--- a/lib/matplotlib/backends/backend_agg.py
+++ b/lib/matplotlib/backends/backend_agg.py
@@ -280,6 +280,7 @@ def buffer_rgba(self):
     def tostring_argb(self):
         return np.asarray(self._renderer).take([3, 0, 1, 2], axis=2).tobytes()
 
+    @_api.deprecated("3.8")
     def tostring_rgb(self):
         return np.asarray(self._renderer).take([0, 1, 2], axis=2).tobytes()
 
@@ -414,6 +415,7 @@ def get_renderer(self, cleared=False):
             self.renderer.clear()
         return self.renderer
 
+    @_api.deprecated("3.8")
     def tostring_rgb(self):
         """
         Get the image as RGB `bytes`.