You can even use conditional formatting with the below formula:

=ISERR(MONTH($F$9))

and put some color like red. So any cell where the data is not in date
format will, change to red color.

but this formatting and the solution by david will not work if somebody
enters 1/2/2008 (1st feb 2008) instead of 2/1/2008 (2nd jan 2008).

--
Kind Regards,
Satti Charvak
Only an Excel Enthusiast
Noida, India


"jvq" wrote:

How can I keep the mm/dd/yy format to display an error or message when other
users enter the wrong date: ie 12/31/20081?