diff --git a/CHANGELOG.md b/CHANGELOG.md
index ddce6a7..a925d33 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,9 @@
 # Changelog
 *[CalVer, YY.month.patch](https://calver.org/)*
 
+## 24.3.3
+- Add ASYNC251: `time.sleep()` in async method.
+
 ## 24.3.2
 - Add ASYNC250: blocking sync call `input()` in async method.
 
diff --git a/README.md b/README.md
index b9cbdb4..fdf01c7 100644
--- a/README.md
+++ b/README.md
@@ -55,7 +55,8 @@ Note: 22X, 23X and 24X has not had asyncio-specific suggestions written.
 - **ASYNC231**: Sync IO call in async function, use `[trio/anyio].wrap_file(...)`. `asyncio` users need to use a library such as [aiofiles](https://pypi.org/project/aiofiles/), or switch to [anyio](https://github.com/agronholm/anyio).
 - **ASYNC232**: Blocking sync call on file object, wrap the file object in `[trio/anyio].wrap_file()` to get an async file object.
 - **ASYNC240**: Avoid using `os.path` in async functions, prefer using `[trio/anyio].Path` objects. `asyncio` users should consider [aiopath](https://pypi.org/project/aiopath) or [anyio](https://github.com/agronholm/anyio).
-- **ASYNC250**: Builtin `input()` should not be called from async function.
+- **ASYNC250**: Builtin `input()` should not be called from async function. Wrap in `[trio/anyio].to_thread.run_sync()` or `asyncio.loop.run_in_executor()`.
+- **ASYNC251**: `time.sleep(...)` should not be called from async function. Use `[trio/anyio/asyncio].sleep(...)`.
 
 ### Warnings disabled by default
 - **ASYNC900**: Async generator without `@asynccontextmanager` not allowed. You might want to enable this on a codebase since async generators are inherently unsafe and cleanup logic might not be performed. See https://github.com/python-trio/flake8-async/issues/211 and https://discuss.python.org/t/using-exceptiongroup-at-anthropic-experience-report/20888/6 for discussion.
diff --git a/flake8_async/visitors/__init__.py b/flake8_async/visitors/__init__.py
index d4f17c4..bd858ec 100644
--- a/flake8_async/visitors/__init__.py
+++ b/flake8_async/visitors/__init__.py
@@ -25,7 +25,7 @@
 utility_visitors: set[type[Flake8AsyncVisitor]] = set()
 utility_visitors_cst: set[type[Flake8AsyncVisitor_cst]] = set()
 
-# Import all visitors so their decorators run, filling the above containers
+# Import all files with visitors so their decorators run, filling the above containers
 # This has to be done at the end to avoid circular imports
 from . import (
     visitor2xx,
diff --git a/flake8_async/visitors/visitor2xx.py b/flake8_async/visitors/visitor2xx.py
index 9005234..099a3ed 100644
--- a/flake8_async/visitors/visitor2xx.py
+++ b/flake8_async/visitors/visitor2xx.py
@@ -398,13 +398,25 @@ def visit_Call(self, node: ast.Call):
 class Visitor25X(Visitor200):
     error_codes: Mapping[str, str] = {
         "ASYNC250": ("Blocking sync call `input()` in async function. Wrap in `{}`."),
+        "ASYNC251": (
+            "Blocking sync call `time.sleep(...)` in async function."
+            " Use `await {}.sleep(...)`."
+        ),
     }
 
     def visit_Call(self, node: ast.Call):
         if not self.async_function:
             return
-        if isinstance(node.func, ast.Name) and node.func.id == "input":
+        func_name = ast.unparse(node.func)
+        if func_name == "input":
+            error_code = "ASYNC250"
             if len(self.library) == 1:
-                self.error(node, wrappers[self.library_str])
+                msg_param = wrappers[self.library_str]
             else:
-                self.error(node, "/".join(wrappers[lib] for lib in self.library))
+                msg_param = "[" + "/".join(wrappers[lib] for lib in self.library) + "]"
+        elif func_name == "time.sleep":
+            error_code = "ASYNC251"
+            msg_param = self.library_str
+        else:
+            return
+        self.error(node, msg_param, error_code=error_code)
diff --git a/tests/eval_files/async251.py b/tests/eval_files/async251.py
new file mode 100644
index 0000000..9dd6836
--- /dev/null
+++ b/tests/eval_files/async251.py
@@ -0,0 +1,13 @@
+# NOAUTOFIX
+
+import time
+from time import sleep
+
+
+async def foo():
+    time.sleep(5) if 5 else None  # ASYNC251: 8, "trio"
+    time.sleep(5)  # ASYNC251: 4, "trio"
+
+    # Not handled due to difficulty tracking imports and not wanting to trigger
+    # false positives. But could definitely be handled by ruff et al.
+    sleep(5)
diff --git a/tests/eval_files/async251_multi_library.py b/tests/eval_files/async251_multi_library.py
new file mode 100644
index 0000000..f736c5d
--- /dev/null
+++ b/tests/eval_files/async251_multi_library.py
@@ -0,0 +1,9 @@
+# BASE_LIBRARY trio
+# NOASYNCIO # tests asyncio without replacing for it
+import trio
+import time
+import asyncio
+
+
+async def foo():
+    time.sleep(5)  # ASYNC251: 4, "[trio/asyncio]"