You want Countif. If your IDs are in column A, use:
=Countif(A:A,a1)
and copy down.

Any result more than one means a duplicated ID.

Regards,
Fred

"Noetic76" wrote in message
...
Hi, I have a list of documents with unique IDs that were delivered;
electronically, posted or faxed. There are duplicates in the ID column
because some docs were posted AND sent electronically - I need to isolate
ID
numbers that are duplicated by multiple-delivery methods. Can a vlookup do
this?
very much a newbie with lookup, and the list is very big...
thanks!