diff --git a/datasette/utils/asgi.py b/datasette/utils/asgi.py
index 2d4a6cf..8c8eaa0 100644
--- a/datasette/utils/asgi.py
+++ b/datasette/utils/asgi.py
@@ -1,4 +1,5 @@
 import asyncio
+import functools
 import json
 import re
 from http.cookies import Morsel, SimpleCookie
@@ -96,6 +97,19 @@ class _RequestHeaders(dict):
         return super().__contains__(key.lower())
 
 
+def _parse_cookie_header(cookie_header):
+    cookies = SimpleCookie()
+    cookies.load(cookie_header)
+    return {key: value.value for key, value in cookies.items()}
+
+
+# Browsers send the same Cookie header on every request, and the header is
+# read several times per request (router, actor_from_request, templates).
+# Longer headers are not memoized, so the memo cannot pin much memory.
+_MEMOIZED_COOKIE_HEADER_MAX_LENGTH = 8192
+_memoized_parse_cookie_header = functools.lru_cache(maxsize=128)(_parse_cookie_header)
+
+
 class Request:
     def __init__(self, scope, receive, max_post_body_bytes=DEFAULT_MAX_POST_BODY_BYTES):
         self.scope = scope
@@ -136,9 +150,11 @@ class Request:
 
     @property
     def cookies(self):
-        cookies = SimpleCookie()
-        cookies.load(self.headers.get("cookie", ""))
-        return {key: value.value for key, value in cookies.items()}
+        cookie_header = self.headers.get("cookie", "")
+        if len(cookie_header) > _MEMOIZED_COOKIE_HEADER_MAX_LENGTH:
+            return _parse_cookie_header(cookie_header)
+        # A copy, so callers cannot modify the memoized result
+        return dict(_memoized_parse_cookie_header(cookie_header))
 
     @property
     def path(self):
diff --git a/tests/test_internals_request.py b/tests/test_internals_request.py
index 91ef368..276f996 100644
--- a/tests/test_internals_request.py
+++ b/tests/test_internals_request.py
@@ -299,6 +299,26 @@ def test_request_url_vars():
     ).url_vars
 
 
+def test_request_cookies():
+    scope = {"headers": [(b"cookie", b"a=1; b=two")]}
+    request = Request(scope, None)
+    cookies = request.cookies
+    assert cookies == {"a": "1", "b": "two"}
+    # Modifying the returned cookies does not affect later lookups
+    cookies["a"] = "changed"
+    assert request.cookies == {"a": "1", "b": "two"}
+    assert Request(dict(scope), None).cookies == {"a": "1", "b": "two"}
+    request.scope = dict(scope, headers=[(b"cookie", b"c=3")])
+    assert request.cookies == {"c": "3"}
+    assert Request({}, None).cookies == {}
+    # Very long Cookie headers are parsed but not memoized
+    long_value = "x" * 10000
+    long_request = Request(
+        {"headers": [(b"cookie", f"big={long_value}".encode())]}, None
+    )
+    assert long_request.cookies == {"big": long_value}
+
+
 @pytest.mark.parametrize(
     "path,query_string,expected_full_path",
     [("/", "", "/"), ("/", "foo=bar", "/?foo=bar"), ("/foo", "bar", "/foo?bar")],