diff --git a/lib/matplotlib/axes/_secondary_axes.py b/lib/matplotlib/axes/_secondary_axes.py
index 08e706bba245..b373f2bd8ffd 100644
--- a/lib/matplotlib/axes/_secondary_axes.py
+++ b/lib/matplotlib/axes/_secondary_axes.py
@@ -329,6 +329,11 @@ def set_color(self, color):
 Returns
 -------
 ax : axes._secondary_axes.SecondaryAxis
+    The returned Axes is overlaid on top of the original Axes and all
+    components except for the complementary axis are hidden. You may modify
+    the complementary axis, e.g. by setting ticks or an axis label. However,
+    it is not designed to hold data, so that you should not call any
+    plotting methods on it.
 
 Other Parameters
 ----------------