If you really have duplicates in the recordset, eliminate them by changing the query to a totals query so you can use group by to eliminate them.
If the duplicates are caused because you are making a report based on a query that joins two tables in a one-to-many relationship, add a group header and move the "duplicate" fields into the group header. In the group footer, add a new control with a value of
=1
and set the RunningSum property to over group. This will allow you to count the one-side records. Alternatively, change the report to a main report for the one-side data and a sub report for the many-side data.