diff --git a/django/contrib/auth/models.py b/django/contrib/auth/models.py
index 0be8875412..681cf1422a 100644
--- a/django/contrib/auth/models.py
+++ b/django/contrib/auth/models.py
@@ -103,9 +103,25 @@ class Group(models.Model):
 
 class UserManager(models.Manager):
     def create_user(self, username, email, password=None):
-        "Creates and saves a User with the given username, e-mail and password."
+        """
+        Creates and saves a User with the given username, e-mail and password.
+        """
+
         now = datetime.datetime.now()
-        user = self.model(None, username, '', '', email.strip().lower(), 'placeholder', False, True, False, now, now)
+        
+        # Normalize the address by lowercasing the domain part of the email
+        # address.
+        try:
+            email_name, domain_part = email.strip().split('@', 1)
+        except ValueError:
+            pass
+        else:
+            email = '@'.join([email_name, domain_part.lower()])
+
+        user = self.model(username=username, email=email, is_staff=False,
+                         is_active=True, is_superuser=False, last_login=now,
+                         date_joined=now)
+
         if password:
             user.set_password(password)
         else:
diff --git a/django/contrib/auth/tests/forms.py b/django/contrib/auth/tests/forms.py
index a6ab2c448b..05a8a3f094 100644
--- a/django/contrib/auth/tests/forms.py
+++ b/django/contrib/auth/tests/forms.py
@@ -219,4 +219,13 @@ True
 >>> form.cleaned_data['email']
 u'jsmith3@example.com'
 
+# bug #5605, preserve the case of the user name (before the @ in the email address)
+# when creating a user.
+>>> user = User.objects.create_user('test2', 'tesT@EXAMple.com', 'test')
+>>> user.email
+'tesT@example.com'
+>>> user = User.objects.create_user('test3', 'tesT', 'test')
+>>> user.email
+'tesT'
+
 """
diff --git a/docs/topics/auth.txt b/docs/topics/auth.txt
index 0ff2ee6f5e..ddf8c4834c 100644
--- a/docs/topics/auth.txt
+++ b/docs/topics/auth.txt
@@ -293,10 +293,13 @@ Manager functions
     .. method:: models.UserManager.create_user(username, email, password=None)
 
         Creates, saves and returns a :class:`~django.contrib.auth.models.User`.
-        The :attr:`~django.contrib.auth.models.User.username`,
-        :attr:`~django.contrib.auth.models.User.email` and
-        :attr:`~django.contrib.auth.models.User.password` are set as given, and the
-        :class:`~django.contrib.auth.models.User` gets ``is_active=True``.
+        
+        The :attr:`~django.contrib.auth.models.User.username` and
+        :attr:`~django.contrib.auth.models.User.password` are set as given. The
+        domain portion of :attr:`~django.contrib.auth.models.User.email` is
+        automatically convered to lowercase, and the returned
+        :class:`~django.contrib.auth.models.User` object will have
+        :attr:`~models.User.is_active` set to ``True``.
 
         If no password is provided,
         :meth:`~django.contrib.auth.models.User.set_unusable_password()` will