diff --git a/doc/source/reference/extensions.rst b/doc/source/reference/extensions.rst
index 83f830bb11198..e412793a328a3 100644
--- a/doc/source/reference/extensions.rst
+++ b/doc/source/reference/extensions.rst
@@ -49,6 +49,7 @@ objects.
       api.extensions.ExtensionArray.copy
       api.extensions.ExtensionArray.view
       api.extensions.ExtensionArray.dropna
+      api.extensions.ExtensionArray.duplicated
       api.extensions.ExtensionArray.equals
       api.extensions.ExtensionArray.factorize
       api.extensions.ExtensionArray.fillna