Knowledge of the anatomy of the median nerve is important in surgery of the palmar aspect of the hand. The purpose of our study was to investigate the ramification pattern of the thenar branch before entering the thenar fascia and the distribution of the terminal branches in the thenar musculature. The observations were carried out on 144 hands of 74 dissecting room cadavers. According to the number of the thenar branches entering the thenar fascia we classified our specimens into four types. In 121 hands (84%, Group 1) the thenar branch piercing the thenar fascia was a single trunk. In 19 hands (13.2%, Group 11) two branches; in three (2.1%; Group III), three branches; and in one hand (0.7%; Group IV), four branches were identified entering the thenar fascia. Accessory thenar nerve was found in 8.3% of hands. The further division of each branch to its terminal branches was investigated in detail. Our results show that the more the number of thenar branches entering the thenar fascia, the less the terminal branching. Because more than one branch was seen in 16% of the specimens, meticulous dissection is required for preventing injury of the thenar branches before entering the thenar fascia. (c) 2005 Wiley-Liss, Inc.