An apparatus and method that provide an improved method of marking a patient requiring an endourologic procedure such as an ureteroscopy are disclosed. The apparatus is an adhesively-backed sheet with a radiopaque marking symbol designed to eliminate risk of a wrong site surgery by creating a visible, unambiguous marking symbol on an intraoperative medical image. The marker sheet is removably applied to the correct side of the patient's body on the groin or abdomen area before the patient is draped for surgery. The marker is visible to the naked eye before it is covered by drapes and visible on an X-ray or other intra operative imaging device whether covered by drapes or not. The visible marking symbol indicia on the X-ray will be unambiguous and will communicate whether the procedure should or should not be performed on that location.