=SUM(--(FREQUENCY(IF((D5:D2000<"")*(O5:O2000<""),MATCH( D5:D2000,D5:D2000,0)),ROW(INDIRECT("1:"&ROWS(D5:D2 000))))0))

this is an array formula, so commit with Ctrl-Shift-Enter, not just Enter

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HTH

Bob

"Sarah (OGI)" wrote in message
...
I have a spreadsheet whereby I need to be able to count how many unique
items
are in column D (D5 onwards), where each corresponding value in column O
is a
non-blank.

Is there an easy way to do this and if so, how?

Many thanks in advance.