During the superficial dissection of the pectoral region and the arm, an abnormal biceps brachii muscle was observed unilaterally. This muscle had three heads. Whereas the short and long heads had their normal origin, the accessory head originated from the anterior surface of the distal part of the pectoralis major muscle, which formed the anterior axillary fold. To our knowledge, this variation has not been previously described. Innervation and vascular supply of this accessory head was from the musculocutaneous nerve and the brachial artery, respectively.