CPT modifier used for a bilateral procedure. Unless otherwise identified in the listings, bilateral procedures requiring a separate incision performed during the same operative session should be identified by the appropriate five-digit code describing the first procedure. The second (bilateral) procedure is identified by adding modifier -50 to the procedure number. It is important to read each surgical description carefully to look for the word “bilateral.” A bilateral modifier on a unilateral procedure code indicates that the procedure was performed on both sides of a paired organ during the same operative session.