The biceps brachii is a muscle of the anterior compartment of the arm that has two proximal heads, the long head and the short head. However, variations in the number and morphology of this muscle have been reported, such as the presence of a third head. The aim of this study was to investigate the incidence, origin, insertion and innervation of the third head of biceps brachii in human cadavers. The arms of 40 adult cadavers were dissected and examined for the presence of the third head of biceps brachii. The results showed that four cadavers (10%) had a third head of biceps brachii, two on the right side and two on the left side. All the third heads originated from the humerus, below the insertion of coracobrachialis, and inserted into the radial tuberosity along with the long and short heads. The third heads were innervated by the musculocutaneous nerve. The knowledge of the existence and variations of the third head of biceps brachii may be important for clinical diagnosis, surgical procedures and anatomical education.