MemberUsername = Username field

I would put the code in the Click event for the Button before processing the entered data.

If IsNull(MemberUsername) or MemberUsername = "" Then
    MsgBox "Username must not be left blank."
    MemberUsername.SetFocus
    Exit Sub
End If

Thanks Kevin, that's great. Working but it doesn't wotk on the combo boxes: Region and Hospital. These are cascading combo boxes. Any idea??? Thanks!

The Default Value in the table is probably zero (0) so check for that instead of the empty string.

You can also .Dropdown if you want them to open ready to pick a value.

Thanks Kevin, it works and I also applied .dropdown, thanks to Alex. I have seen the videos about the save button and autosave. But I want the user to be able to "not save" and exit the form. For example if the user fills in the username and password but not the rest. I don't want username and password saves to the table. How can I do that? Thanks.