A case of compression of the posterior branch of the radial nerve by a lipoma is reported. This case is unusual because of the large size of the tumor (13 cm x 6 cm) and the interest of CT to exclude a liposarcoma. The risk of liposarcoma is greater with large size tumors. Reported 27 cases have been analyzed. The posterior branch of the radical nerve is particularly vulnerable because of the anatomic relationships. Thus benign extraneural sof-tissue tumors of the extremities may be responsible of nerves compressions.