diff --git a/src/Umbraco.Cms.Api.Management/Controllers/User/UserOrCurrentUserControllerBase.cs b/src/Umbraco.Cms.Api.Management/Controllers/User/UserOrCurrentUserControllerBase.cs
index 43db8355b7..a6faf7ddbe 100644
--- a/src/Umbraco.Cms.Api.Management/Controllers/User/UserOrCurrentUserControllerBase.cs
+++ b/src/Umbraco.Cms.Api.Management/Controllers/User/UserOrCurrentUserControllerBase.cs
@@ -25,7 +25,7 @@ public abstract class UserOrCurrentUserControllerBase : ManagementApiControllerB
                 .Build()),
             UserOperationStatus.NoUserGroup => BadRequest(problemDetailsBuilder
                 .WithTitle("No User Group Specified")
-                .WithDetail("A user group must be specified to create a user")
+                .WithDetail("A user must be assigned to at least one group")
                 .Build()),
             UserOperationStatus.UserNameIsNotEmail => BadRequest(problemDetailsBuilder
                 .WithTitle("Invalid Username")
diff --git a/src/Umbraco.Core/Services/UserService.cs b/src/Umbraco.Core/Services/UserService.cs
index 718ef1eb69..612e32efde 100644
--- a/src/Umbraco.Core/Services/UserService.cs
+++ b/src/Umbraco.Core/Services/UserService.cs
@@ -883,7 +883,7 @@ internal partial class UserService : RepositoryService, IUserService
             return UserOperationStatus.DuplicateUserName;
         }
 
-        if(model.UserGroupKeys.Count == 0)
+        if (model.UserGroupKeys.Count == 0)
         {
             return UserOperationStatus.NoUserGroup;
         }
@@ -912,6 +912,13 @@ internal partial class UserService : RepositoryService, IUserService
             return Attempt.FailWithStatus<IUser?, UserOperationStatus>(UserOperationStatus.MissingUser, existingUser);
         }
 
+        // A user must remain assigned to at least one group.
+        if (model.UserGroupKeys.Count == 0)
+        {
+            scope.Complete();
+            return Attempt.FailWithStatus<IUser?, UserOperationStatus>(UserOperationStatus.NoUserGroup, existingUser);
+        }
+
         // User names can only contain the configured allowed characters. This is validated by ASP.NET Identity on create
         // as the setting is applied to the BackOfficeIdentityOptions, but we need to check ourselves for updates.
         var allowedUserNameCharacters = _securitySettings.AllowedUserNameCharacters;
diff --git a/tests/Umbraco.Tests.AcceptanceTest/tests/DefaultConfig/Users/User.spec.ts b/tests/Umbraco.Tests.AcceptanceTest/tests/DefaultConfig/Users/User.spec.ts
index 3b8b6b34ec..0ede3be26b 100644
--- a/tests/Umbraco.Tests.AcceptanceTest/tests/DefaultConfig/Users/User.spec.ts
+++ b/tests/Umbraco.Tests.AcceptanceTest/tests/DefaultConfig/Users/User.spec.ts
@@ -642,4 +642,4 @@ test.skip('cannot remove all user group from a user', {tag: '@release'}, async (
 
   // Assert
   await umbracoUi.user.isErrorNotificationVisible();
-});
\ No newline at end of file
+});
diff --git a/tests/Umbraco.Tests.Integration/Umbraco.Core/Services/UserServiceCrudTests.Update.cs b/tests/Umbraco.Tests.Integration/Umbraco.Core/Services/UserServiceCrudTests.Update.cs
index 4b5cc29fee..f2d8ab68b8 100644
--- a/tests/Umbraco.Tests.Integration/Umbraco.Core/Services/UserServiceCrudTests.Update.cs
+++ b/tests/Umbraco.Tests.Integration/Umbraco.Core/Services/UserServiceCrudTests.Update.cs
@@ -151,7 +151,21 @@ internal sealed partial class UserServiceCrudTests
             Assert.AreEqual(email, updatedUser.Email);
             Assert.AreEqual(name, updatedUser.Name);
         });
+    }
 
+    [Test]
+    public async Task Cannot_Update_User_To_Have_No_Groups()
+    {
+        var userService = CreateUserService(securitySettings: new SecuritySettings { UsernameIsEmail = false });
+
+        var (updateModel, createdUser) = await CreateUserForUpdate(userService);
+
+        updateModel.UserGroupKeys.Clear();
+
+        var updateAttempt = await userService.UpdateAsync(Constants.Security.SuperUserKey, updateModel);
+
+        Assert.IsFalse(updateAttempt.Success);
+        Assert.AreEqual(UserOperationStatus.NoUserGroup, updateAttempt.Status);
     }
 
     [Test]