diff --git a/.changeset/fix_optional_bodies.md b/.changeset/fix_optional_bodies.md
@@ -0,0 +1,13 @@
+---
+default: patch
+---
+
+# Fix optional bodies
+
+If a body is not required (the default), it will now:
+
+1. Have `Unset` as part of its type annotation.
+2. Default to a value of `UNSET`
+3. Not be included in the request if it is `UNSET`
+
+Thanks @orelmaliach for the report! Fixes #1354
diff --git a/end_to_end_tests/baseline_openapi_3.0.json b/end_to_end_tests/baseline_openapi_3.0.json
@@ -104,6 +104,30 @@
         }
       }
     },
+    "/bodies/optional": {
+      "post": {
+        "tags": [
+          "bodies"
+        ],
+        "description": "Test optional request body",
+        "operationId": "optional-body",
+        "requestBody": {
+          "required": false,
+          "content": {
+            "application/json": {
+              "schema": {
+                "type": "object"
+              }
+            }
+          }
+        },
+        "responses": {
+          "200": {
+            "description": "OK"
+          }
+        }
+      }
+    },
     "/tests/": {
       "get": {
         "tags": [
@@ -1813,6 +1837,47 @@
           }
         }
       }
+    },
+    "/types/unions/duplicate-types": {
+      "post": {
+        "title": "duplicate union members",
+        "requestBody": {
+          "description": "The request body",
+          "content": {
+            "application/json": {
+              "schema": {
+                "oneOf": [
+                  {
+                    "$ref": "#/components/schemas/AModel"
+                  },
+                  {
+                    "$ref": "#/components/schemas/AModel"
+                  }
+                ]
+              }
+            }
+          }
+        },
+        "responses": {
+          "200": {
+            "description": "Successful response",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "oneOf": [
+                    {
+                      "$ref": "#/components/schemas/AModel"
+                    },
+                    {
+                      "$ref": "#/components/schemas/AModel"
+                    }
+                  ]
+                }
+              }
+            }
+          }
+        }
+      }
     }
   },
   "components": {

diff --git a/end_to_end_tests/baseline_openapi_3.1.yaml b/end_to_end_tests/baseline_openapi_3.1.yaml
@@ -100,6 +100,30 @@ info:
       }
     }
   },
+  "/bodies/optional": {
+    "post": {
+      "tags": [
+        "bodies"
+      ],
+      "description": "Test optional request body",
+      "operationId": "optional-body",
+      "requestBody": {
+        "required": false,
+        "content": {
+          "application/json": {
+            "schema": {
+              "type": "object"
+            }
+          }
+        }
+      },
+      "responses": {
+        "200": {
+          "description": "OK"
+        }
+      }
+    }
+  },
   "/tests/": {
     "get": {
       "tags": [
@@ -1779,6 +1803,39 @@ info:
         }
       }
     }
+  },
+  "/types/unions/duplicate-types": {
+    "post": {
+      "title": "duplicate union members",
+      "requestBody": {
+        "description": "The request body",
+        "content": {
+          "application/json": {
+            "schema": {
+              "oneOf": [
+                {"$ref": "#/components/schemas/AModel"},
+                {"$ref": "#/components/schemas/AModel"}
+              ]
+            }
+          }
+        }
+      },
+      "responses": {
+        "200": {
+          "description": "Successful response",
+          "content": {
+            "application/json": {
+              "schema": {
+                "oneOf": [
+                  {"$ref": "#/components/schemas/AModel"},
+                  {"$ref": "#/components/schemas/AModel"}
+                ]
+              }
+            }
+          }
+        }
+      }
+    }
   }
 }
 "components":

diff --git a/end_to_end_tests/custom-templates-golden-record/my_test_api_client/api/bodies/__init__.py b/end_to_end_tests/custom-templates-golden-record/my_test_api_client/api/bodies/__init__.py
@@ -2,7 +2,7 @@
 
 import types
 
-from . import json_like, post_bodies_multiple, refs
+from . import json_like, optional_body, post_bodies_multiple, refs
 
 
 class BodiesEndpoints:
@@ -26,3 +26,10 @@ def refs(cls) -> types.ModuleType:
         Test request body defined via ref
         """
         return refs
+
+    @classmethod
+    def optional_body(cls) -> types.ModuleType:
+        """
+        Test optional request body
+        """
+        return optional_body
diff --git a/end_to_end_tests/custom-templates-golden-record/my_test_api_client/api/default/__init__.py b/end_to_end_tests/custom-templates-golden-record/my_test_api_client/api/default/__init__.py
@@ -7,6 +7,7 @@
     get_models_allof,
     get_models_oneof_with_required_const,
     post_common_parameters,
+    post_types_unions_duplicate_types,
     reserved_parameters,
 )
 
@@ -31,3 +32,7 @@ def get_models_allof(cls) -> types.ModuleType:
     @classmethod
     def get_models_oneof_with_required_const(cls) -> types.ModuleType:
         return get_models_oneof_with_required_const
+
+    @classmethod
+    def post_types_unions_duplicate_types(cls) -> types.ModuleType:
+        return post_types_unions_duplicate_types
diff --git a/end_to_end_tests/functional_tests/generated_code_execution/test_docstrings.py b/end_to_end_tests/functional_tests/generated_code_execution/test_docstrings.py
@@ -152,7 +152,7 @@ def test_response_union_type(self, post_simple_thing_sync):
 
     def test_request_body(self, post_simple_thing_sync):
         assert DocstringParser(post_simple_thing_sync).get_section("Args:") == [
-            "body (Thing): The thing."
+            "body (Thing | Unset): The thing."
         ]
 
     def test_params(self, get_attribute_by_index_sync):

diff --git a/end_to_end_tests/golden-record/my_test_api_client/api/bodies/json_like.py b/end_to_end_tests/golden-record/my_test_api_client/api/bodies/json_like.py
@@ -6,12 +6,12 @@
 from ... import errors
 from ...client import AuthenticatedClient, Client
 from ...models.json_like_body import JsonLikeBody
-from ...types import Response
+from ...types import UNSET, Response, Unset
 
 
 def _get_kwargs(
     *,
-    body: JsonLikeBody,
+    body: JsonLikeBody | Unset = UNSET,
 ) -> dict[str, Any]:
     headers: dict[str, Any] = {}
 
@@ -20,7 +20,8 @@ def _get_kwargs(
         "url": "/bodies/json-like",
     }
 
-    _kwargs["json"] = body.to_dict()
+    if not isinstance(body, Unset):
+        _kwargs["json"] = body.to_dict()
 
     headers["Content-Type"] = "application/vnd+json"
 
@@ -50,12 +51,12 @@ def _build_response(*, client: AuthenticatedClient | Client, response: httpx.Res
 def sync_detailed(
     *,
     client: AuthenticatedClient | Client,
-    body: JsonLikeBody,
+    body: JsonLikeBody | Unset = UNSET,
 ) -> Response[Any]:
     """A content type that works like json but isn't application/json
 
     Args:
-        body (JsonLikeBody):
+        body (JsonLikeBody | Unset):
 
     Raises:
         errors.UnexpectedStatus: If the server returns an undocumented status code and Client.raise_on_unexpected_status is True.
@@ -79,12 +80,12 @@ def sync_detailed(
 async def asyncio_detailed(
     *,
     client: AuthenticatedClient | Client,
-    body: JsonLikeBody,
+    body: JsonLikeBody | Unset = UNSET,
 ) -> Response[Any]:
     """A content type that works like json but isn't application/json
 
     Args:
-        body (JsonLikeBody):
+        body (JsonLikeBody | Unset):
 
     Raises:
         errors.UnexpectedStatus: If the server returns an undocumented status code and Client.raise_on_unexpected_status is True.

diff --git a/end_to_end_tests/golden-record/my_test_api_client/api/bodies/optional_body.py b/end_to_end_tests/golden-record/my_test_api_client/api/bodies/optional_body.py
@@ -0,0 +1,104 @@
+from http import HTTPStatus
+from typing import Any
+
+import httpx
+
+from ... import errors
+from ...client import AuthenticatedClient, Client
+from ...models.optional_body_body import OptionalBodyBody
+from ...types import UNSET, Response, Unset
+
+
+def _get_kwargs(
+    *,
+    body: OptionalBodyBody | Unset = UNSET,
+) -> dict[str, Any]:
+    headers: dict[str, Any] = {}
+
+    _kwargs: dict[str, Any] = {
+        "method": "post",
+        "url": "/bodies/optional",
+    }
+
+    if not isinstance(body, Unset):
+        _kwargs["json"] = body.to_dict()
+
+    headers["Content-Type"] = "application/json"
+
+    _kwargs["headers"] = headers
+    return _kwargs
+
+
+def _parse_response(*, client: AuthenticatedClient | Client, response: httpx.Response) -> Any | None:
+    if response.status_code == 200:
+        return None
+
+    if client.raise_on_unexpected_status:
+        raise errors.UnexpectedStatus(response.status_code, response.content)
+    else:
+        return None
+
+
+def _build_response(*, client: AuthenticatedClient | Client, response: httpx.Response) -> Response[Any]:
+    return Response(
+        status_code=HTTPStatus(response.status_code),
+        content=response.content,
+        headers=response.headers,
+        parsed=_parse_response(client=client, response=response),
+    )
+
+
+def sync_detailed(
+    *,
+    client: AuthenticatedClient | Client,
+    body: OptionalBodyBody | Unset = UNSET,
+) -> Response[Any]:
+    """Test optional request body
+
+    Args:
+        body (OptionalBodyBody | Unset):
+
+    Raises:
+        errors.UnexpectedStatus: If the server returns an undocumented status code and Client.raise_on_unexpected_status is True.
+        httpx.TimeoutException: If the request takes longer than Client.timeout.
+
+    Returns:
+        Response[Any]
+    """
+
+    kwargs = _get_kwargs(
+        body=body,
+    )
+
+    response = client.get_httpx_client().request(
+        **kwargs,
+    )
+
+    return _build_response(client=client, response=response)
+
+
+async def asyncio_detailed(
+    *,
+    client: AuthenticatedClient | Client,
+    body: OptionalBodyBody | Unset = UNSET,
+) -> Response[Any]:
+    """Test optional request body
+
+    Args:
+        body (OptionalBodyBody | Unset):
+
+    Raises:
+        errors.UnexpectedStatus: If the server returns an undocumented status code and Client.raise_on_unexpected_status is True.
+        httpx.TimeoutException: If the request takes longer than Client.timeout.
+
+    Returns:
+        Response[Any]
+    """
+
+    kwargs = _get_kwargs(
+        body=body,
+    )
+
+    response = await client.get_async_httpx_client().request(**kwargs)
+
+    return _build_response(client=client, response=response)