Select your data, with cell A1 as the activecell.

Go into Format = Conditional formatting

change the "Cell Value is" dropdown to show "Formula is"

in the textbox enter a formula like

=Countif($A:$A,A1)1

Then click on the format button and in the patterns tab, select Blue

then OK your way out.

--
Regards,
Tom Ogilvy


Gareth wrote in message
...
I have customer numbers in column A of a sheet. I would like to be able
to
colour the cell blue for instances when the same customer number occurs
twice.

Thanks in advance.

Spike