diff --git a/files/en-us/web/api/formdata/entries/index.md b/files/en-us/web/api/formdata/entries/index.md
index 71cd4ed75f41d93..ff88957bad9da72 100644
--- a/files/en-us/web/api/formdata/entries/index.md
+++ b/files/en-us/web/api/formdata/entries/index.md
@@ -10,6 +10,9 @@ browser-compat: api.FormData.entries
 
 The **`FormData.entries()`** method returns an [iterator](/en-US/docs/Web/JavaScript/Reference/Iteration_protocols) which iterates through all key/value pairs contained in the {{domxref("FormData")}}. The key of each pair is a string, and the value is either a string or a {{domxref("Blob")}}.
 
+> [!NOTE]
+> Unlike [`Map`](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map) entries, `FormData` entries are not necessarily unique by key. A form can contain multiple elements with the same name, so the same key may appear in more than one pair while iterating. To retrieve all values associated with a single key, use the {{domxref("FormData.getAll()", "getAll()")}} method (or {{domxref("FormData.get()", "get()")}} for only the first value).
+
 ## Syntax
 
 ```js-nolint
diff --git a/files/en-us/web/api/formdata/keys/index.md b/files/en-us/web/api/formdata/keys/index.md
index 09a273885fe9ebf..51e2e8c787359a9 100644
--- a/files/en-us/web/api/formdata/keys/index.md
+++ b/files/en-us/web/api/formdata/keys/index.md
@@ -10,6 +10,9 @@ browser-compat: api.FormData.keys
 
 The **`FormData.keys()`** method returns an [iterator](/en-US/docs/Web/JavaScript/Reference/Iteration_protocols) which iterates through all keys contained in the {{domxref("FormData")}}. The keys are strings.
 
+> [!NOTE]
+> Unlike [`Map`](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map) keys, `FormData` keys are not necessarily unique. A form can contain multiple elements with the same name, so the same key may appear more than once while iterating. To retrieve all values associated with a single key, use the {{domxref("FormData.getAll()", "getAll()")}} method (or {{domxref("FormData.get()", "get()")}} for only the first value).
+
 ## Syntax
 
 ```js-nolint
diff --git a/files/en-us/web/api/formdata/values/index.md b/files/en-us/web/api/formdata/values/index.md
index a422cd53c0f9c4f..92105aa21553b12 100644
--- a/files/en-us/web/api/formdata/values/index.md
+++ b/files/en-us/web/api/formdata/values/index.md
@@ -10,6 +10,9 @@ browser-compat: api.FormData.values
 
 The **`FormData.values()`** method returns an [iterator](/en-US/docs/Web/JavaScript/Reference/Iteration_protocols) which iterates through all values contained in the {{domxref("FormData")}}. The values are strings or {{domxref("Blob")}} objects.
 
+> [!NOTE]
+> `FormData` keys are not necessarily unique. A form can contain multiple elements with the same name, so values sharing one key each appear while iterating. To retrieve all values associated with a single key, use the {{domxref("FormData.getAll()", "getAll()")}} method (or {{domxref("FormData.get()", "get()")}} for only the first value).
+
 ## Syntax
 
 ```js-nolint