Try the following...

=SUM(IF(FREQUENCY(IF((A1:A5<"")*(B1:B5="1/1/2004"+0),MATCH(A1:A5,A1:A5,0
)),ROW(INDIRECT("1:"&ROWS(A1:A5))))0,1,0))

....confirmed with CONTROL+SHIFT+ENTER, not just ENTER.

Hope this helps!

In article ,
"Naomi" wrote:

D F

Client 1 Jan-04
Client 2 Feb-04
Client 1 Jan-04
Client 2 Jan-04
Client 4 Jan-04

I would hope for this to give me a value of 3 but instead I get a value of
2.5?!
ie. Unique clients that also have Jan-04 in col F.
Thanks.