The Nervus peroneus profundus accessorius was described by Ruge (1878) in the lower mammals and for the first time identified by Bryce (1897) in man. It is an accessory terminal branch of the superficial peroneal (musculocutaneous) nerve which winds round the lateral malleolus beneath the tendons of the peronei muscles and reaches the dorsum of the foot; there it often supplies the lateral portion of the extensor digitorum brevis muscle. In further investigations this nerve has been traced in 21.2% of subjects resp. in 13.5% of legs. This nerve, however, is not the only accessory branch of the common peroneal nerve: In 14 out of 140 subjects (10%) resp. in 22 out of 280 legs (7.9%) a Nervus peroneus superficialis accessorius has been found. This nerve pierces the anterior crural intermuscular septum either in common with deep peroneal (anterior tibial) nerve or at a lower point. Then it descends in front of the septum rarely giving off muscular branches to the extensor digitorum longus and peroneus tertius muscles; in the lower half of the leg it pierces the crural fascia, passes in front of the ankle joint and becomes the medial cutaneous nerve of the dorsum of the foot. This accessory superficial peroneal nerve may be of importance in surgery of the leg and foot.