diff --git a/django/utils/regex_helper.py b/django/utils/regex_helper.py
index 9e57ff8f15..b06acb0191 100644
--- a/django/utils/regex_helper.py
+++ b/django/utils/regex_helper.py
@@ -5,10 +5,6 @@ Used internally by Django and not intended for external use.
 This is not, and is not intended to be, a complete reg-exp decompiler. It
 should be good enough for a large class of URLS, however.
 """
-import warnings
-
-from django.utils.deprecation import RemovedInDjango21Warning
-
 # Mapping of an escape character to a representative of that class. So, e.g.,
 # "\w" is replaced by "x" in a reverse URL. A value of None means to ignore
 # this sequence. Any missing key is mapped to itself.
@@ -121,12 +117,6 @@ def normalize(pattern):
                         # All of these are ignorable. Walk to the end of the
                         # group.
                         walk_to_end(ch, pattern_iter)
-                    elif ch in 'iLmsu#':
-                        warnings.warn(
-                            'Using (?%s) in url() patterns is deprecated.' % ch,
-                            RemovedInDjango21Warning
-                        )
-                        walk_to_end(ch, pattern_iter)
                     elif ch == ':':
                         # Non-capturing group
                         non_capturing_groups.append(len(result))
diff --git a/docs/releases/2.1.txt b/docs/releases/2.1.txt
index fd56560365..d4dbc8fc3a 100644
--- a/docs/releases/2.1.txt
+++ b/docs/releases/2.1.txt
@@ -256,3 +256,5 @@ how to remove usage of these features.
   ``django.utils.cache.patch_response_headers()`` no longer set ETags.
 
 * The ``Model._meta.has_auto_field`` attribute is removed.
+
+* Support for regular expression groups with ``iLmsu#`` in ``url()`` is removed.
diff --git a/tests/urlpatterns_reverse/test_deprecated.py b/tests/urlpatterns_reverse/test_deprecated.py
deleted file mode 100644
index c918dd5a17..0000000000
--- a/tests/urlpatterns_reverse/test_deprecated.py
+++ /dev/null
@@ -1,33 +0,0 @@
-import warnings
-
-from django.conf.urls import url
-from django.test import SimpleTestCase, override_settings
-from django.urls import reverse
-
-from .views import empty_view
-
-urlpatterns = [
-    url(r'^(?i)CaseInsensitive/(\w+)', empty_view, name="insensitive"),
-    url(r'^(?i)test/2/?$', empty_view, name="test2"),
-]
-
-
-@override_settings(ROOT_URLCONF='urlpatterns_reverse.test_deprecated')
-class URLPatternReverse(SimpleTestCase):
-
-    def test_urlpattern_reverse(self):
-        test_data = (
-            ('insensitive', '/CaseInsensitive/fred', ['fred'], {}),
-            ('test2', '/test/2', [], {}),
-        )
-        with warnings.catch_warnings(record=True) as warns:
-            warnings.simplefilter('always')
-            warnings.filterwarnings(
-                'ignore', 'Flags not at the start',
-                DeprecationWarning, module='django.urls.resolvers'
-            )
-            for i, (name, expected, args, kwargs) in enumerate(test_data):
-                got = reverse(name, args=args, kwargs=kwargs)
-                self.assertEqual(got, expected)
-                msg = str(warns[i].message)
-                self.assertEqual(msg, 'Using (?i) in url() patterns is deprecated.')
diff --git a/tests/utils_tests/test_regex_helper.py b/tests/utils_tests/test_regex_helper.py
index 93383e1c1a..77bcd5bb35 100644
--- a/tests/utils_tests/test_regex_helper.py
+++ b/tests/utils_tests/test_regex_helper.py
@@ -1,5 +1,4 @@
 import unittest
-import warnings
 
 from django.utils import regex_helper
 
@@ -23,16 +22,6 @@ class NormalizeTests(unittest.TestCase):
         result = regex_helper.normalize(pattern)
         self.assertEqual(result, expected)
 
-    def test_group_ignored(self):
-        pattern = r"(?i)(?L)(?m)(?s)(?u)(?#)"
-        expected = [('', [])]
-        with warnings.catch_warnings(record=True) as warns:
-            warnings.simplefilter('always')
-            result = regex_helper.normalize(pattern)
-        self.assertEqual(result, expected)
-        for i, char in enumerate('iLmsu#'):
-            self.assertEqual(str(warns[i].message), 'Using (?%s) in url() patterns is deprecated.' % char)
-
     def test_group_noncapturing(self):
         pattern = r"(?:non-capturing)"
         expected = [('non-capturing', [])]