diff --git a/gnuviechadmin/osusers/admin.py b/gnuviechadmin/osusers/admin.py
index 8c38f3f..e5d0448 100644
--- a/gnuviechadmin/osusers/admin.py
+++ b/gnuviechadmin/osusers/admin.py
@@ -1,3 +1,24 @@
 from django.contrib import admin
 
-# Register your models here.
+from .models import (
+    AdditionalGroup,
+    Group,
+    Shadow,
+    User,
+)
+
+
+class AdditionalGroupInline(admin.TabularInline):
+    model = AdditionalGroup
+
+
+class ShadowInline(admin.TabularInline):
+    model = Shadow
+
+
+class UserAdmin(admin.ModelAdmin):
+    inlines = [AdditionalGroupInline, ShadowInline]
+
+
+admin.site.register(Group)
+admin.site.register(User, UserAdmin)
diff --git a/gnuviechadmin/osusers/migrations/0002_auto__add_additionalgroup__add_unique_additionalgroup_user_group.py b/gnuviechadmin/osusers/migrations/0002_auto__add_additionalgroup__add_unique_additionalgroup_user_group.py
new file mode 100644
index 0000000..d5ef6d2
--- /dev/null
+++ b/gnuviechadmin/osusers/migrations/0002_auto__add_additionalgroup__add_unique_additionalgroup_user_group.py
@@ -0,0 +1,77 @@
+# -*- coding: utf-8 -*-
+from south.utils import datetime_utils as datetime
+from south.db import db
+from south.v2 import SchemaMigration
+from django.db import models
+
+
+class Migration(SchemaMigration):
+
+    def forwards(self, orm):
+        # Adding model 'AdditionalGroup'
+        db.create_table(u'osusers_additionalgroup', (
+            (u'id', self.gf('django.db.models.fields.AutoField')(primary_key=True)),
+            ('created', self.gf('model_utils.fields.AutoCreatedField')(default=datetime.datetime.now)),
+            ('modified', self.gf('model_utils.fields.AutoLastModifiedField')(default=datetime.datetime.now)),
+            ('user', self.gf('django.db.models.fields.related.ForeignKey')(to=orm['osusers.User'])),
+            ('group', self.gf('django.db.models.fields.related.ForeignKey')(to=orm['osusers.Group'])),
+        ))
+        db.send_create_signal(u'osusers', ['AdditionalGroup'])
+
+        # Adding unique constraint on 'AdditionalGroup', fields ['user', 'group']
+        db.create_unique(u'osusers_additionalgroup', ['user_id', 'group_id'])
+
+
+    def backwards(self, orm):
+        # Removing unique constraint on 'AdditionalGroup', fields ['user', 'group']
+        db.delete_unique(u'osusers_additionalgroup', ['user_id', 'group_id'])
+
+        # Deleting model 'AdditionalGroup'
+        db.delete_table(u'osusers_additionalgroup')
+
+
+    models = {
+        u'osusers.additionalgroup': {
+            'Meta': {'unique_together': "(('user', 'group'),)", 'object_name': 'AdditionalGroup'},
+            'created': ('model_utils.fields.AutoCreatedField', [], {'default': 'datetime.datetime.now'}),
+            'group': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['osusers.Group']"}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'modified': ('model_utils.fields.AutoLastModifiedField', [], {'default': 'datetime.datetime.now'}),
+            'user': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['osusers.User']"})
+        },
+        u'osusers.group': {
+            'Meta': {'object_name': 'Group'},
+            'created': ('model_utils.fields.AutoCreatedField', [], {'default': 'datetime.datetime.now'}),
+            'descr': ('django.db.models.fields.TextField', [], {'blank': 'True'}),
+            'gid': ('django.db.models.fields.PositiveSmallIntegerField', [], {'unique': 'True', 'primary_key': 'True'}),
+            'groupname': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '16'}),
+            'modified': ('model_utils.fields.AutoLastModifiedField', [], {'default': 'datetime.datetime.now'}),
+            'passwd': ('django.db.models.fields.CharField', [], {'max_length': '128', 'blank': 'True'})
+        },
+        u'osusers.shadow': {
+            'Meta': {'object_name': 'Shadow'},
+            'changedays': ('django.db.models.fields.PositiveSmallIntegerField', [], {'null': 'True', 'blank': 'True'}),
+            'created': ('model_utils.fields.AutoCreatedField', [], {'default': 'datetime.datetime.now'}),
+            'expiredays': ('django.db.models.fields.PositiveSmallIntegerField', [], {'default': 'None', 'null': 'True', 'blank': 'True'}),
+            'gracedays': ('django.db.models.fields.PositiveSmallIntegerField', [], {'null': 'True', 'blank': 'True'}),
+            'inactdays': ('django.db.models.fields.PositiveSmallIntegerField', [], {'null': 'True', 'blank': 'True'}),
+            'maxage': ('django.db.models.fields.PositiveSmallIntegerField', [], {'null': 'True', 'blank': 'True'}),
+            'minage': ('django.db.models.fields.PositiveSmallIntegerField', [], {'null': 'True', 'blank': 'True'}),
+            'modified': ('model_utils.fields.AutoLastModifiedField', [], {'default': 'datetime.datetime.now'}),
+            'passwd': ('django.db.models.fields.CharField', [], {'max_length': '128'}),
+            'user': ('django.db.models.fields.related.OneToOneField', [], {'to': u"orm['osusers.User']", 'unique': 'True', 'primary_key': 'True'})
+        },
+        u'osusers.user': {
+            'Meta': {'object_name': 'User'},
+            'created': ('model_utils.fields.AutoCreatedField', [], {'default': 'datetime.datetime.now'}),
+            'gecos': ('django.db.models.fields.CharField', [], {'max_length': '128', 'blank': 'True'}),
+            'group': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['osusers.Group']"}),
+            'homedir': ('django.db.models.fields.CharField', [], {'max_length': '256'}),
+            'modified': ('model_utils.fields.AutoLastModifiedField', [], {'default': 'datetime.datetime.now'}),
+            'shell': ('django.db.models.fields.CharField', [], {'max_length': '64'}),
+            'uid': ('django.db.models.fields.PositiveSmallIntegerField', [], {'unique': 'True', 'primary_key': 'True'}),
+            'username': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '64'})
+        }
+    }
+
+    complete_apps = ['osusers']
\ No newline at end of file
diff --git a/gnuviechadmin/osusers/models.py b/gnuviechadmin/osusers/models.py
index dd16bc8..f760d61 100644
--- a/gnuviechadmin/osusers/models.py
+++ b/gnuviechadmin/osusers/models.py
@@ -1,4 +1,6 @@
 from django.db import models
+from django.core.exceptions import ValidationError
+from django.utils.translation import ugettext as _
 
 from model_utils.models import TimeStampedModel
 
@@ -29,3 +31,16 @@ class Shadow(TimeStampedModel, models.Model):
     inactdays = models.PositiveSmallIntegerField(blank=True, null=True)
     expiredays = models.PositiveSmallIntegerField(blank=True, null=True,
                                                   default=None)
+
+
+class AdditionalGroup(TimeStampedModel, models.Model):
+    user = models.ForeignKey(User)
+    group = models.ForeignKey(Group)
+
+    class Meta:
+        unique_together = ('user', 'group')
+
+    def clean(self):
+        if self.user.group == self.group:
+            raise ValidationError(_(
+                "You can not use a user's primary group."))