A rare case of a four-headed biceps brachii muscle associated with a double piercing of one of the supernumerary heads by the musculocutaneous nerve was observed in the right arm of an 87-year-old female cadaver. One of the supernumerary heads of the biceps brachii originated from the humerus, in the area between the lesser tubercle and the coracobrachialis and brachialis muscles and joined the long head at the level where the latter joined the short head. The second supernumerary head originated from the humerus at the point where the coracobrachialis muscle inserted and joined the biceps brachii tendon and its bicipital aponeurosis at the inferior third of the arm. The musculocutaneous nerve originated from the lateral cord of the brachial plexus and, after piercing the coracobrachialis muscle, coursed along one of the supernumerary heads of the biceps brachii muscle before piercing it from deep to superficial and then again from superficial to deep. It then adopted its normal position between the biceps brachii and brachialis muscles before exiting in the lateral aspect of the arm and continuing as the lateral cutaneous nerve of the forearm.