In addition to Raymondo's suggestion, you can handle it from the query that provides the report's recordset.
Open the query in design view, select the key field (the one that will distinguish the record in both the form and report) and then set its critieria to:
Forms!YourFormName!ControlName
The control name will be for the control (text box, listbox, combobox) that is bound to the key field.
The report will now only show records related to the form's current record.
Cheers, Bill