Results from the query?
Assuming you mean the number of results from the browsers query, then...
Use the NUM-RESULTS function (or attribute if it's dynamic), but... as a FOR EACH browse query initially only grabs a small subset of the results I think you'll need to use PRESELECT - which slows things down.
An alternative would be to open a query of your own before initialising the browse as a PRESELECT using the FIELDS option to return no fields and getting NUM-RESULTS from that. Having no fields returned makes it run quicker, so potentially you'd get better performance than by getting the results from the browse.
AFAIK, there's no ideal solution.
EG
Code:
OPEN QUERY qResults PRESELECT EACH Customer FIELDS NO-LOCK.
MESSAGE NUM-RESULTS ( "qResults" ) VIEW-AS ALERT-BOX INFORMATION.
CLOSE QUERY qResults.