diff --git a/pandas/core/frame.py b/pandas/core/frame.py
index 643974db5f2bf..6a000de1d069a 100644
--- a/pandas/core/frame.py
+++ b/pandas/core/frame.py
@@ -10629,6 +10629,11 @@ def apply(
               If you are just applying a NumPy reduction function this will
               achieve much better performance.
 
+         .. warning::
+
+            When ``raw=True``, the result dtype is inferred from the **first**
+            returned value.
+
         result_type : {'expand', 'reduce', 'broadcast', None}, default None
             These only act when ``axis=1`` (columns):