Or an Option Group?
It's almost always better, and saves the user's time, to prevent wrong data from being entered, rather than fixing it after it's been incorrectly entered.
If space on your Form is limited, you can always arrange an Option Group with the choices available in a straight line, rather than the default 'up-and- down,' configuration...taking up no more space than a Combobox would.
Linq ;0)>
The problem with making anything foolproof...is that fools are so darn ingenious!
All posts/responses based on Access 2003/2007