I can't think of anything that supports this without a formula, but try this
one with Data=Validation, Custom

=AND(LEFT(A1,1)="C",LEN(A1)=16,ISNUMBER(SUBSTITUTE (RIGHT(A1,14),"-","")*1),L
EN(SUBSTITUTE(RIGHT(A1,14),"-",""))=12)

--
Regards,
Tom Ogilvy


"Rob" wrote in message
...
I want to set data validation on cells to only allow:

C-###-#####-#### (# is any digit)

Is there a way I can use the equivalent of an Input Mask, or do I have to
write a big long formula?

Thanks
Rob