Between 1993 and 1995, we operated on 18 patients for split lesions of the peroneal brevis tendon associated with chronic ankle instability. Five patients were competitive athletes, seven were recreational athletes, and six were persons. Symptoms developed in three phases: ankle sprain, chronic instability, and posterolateral pain. The mean delay between sprain and posterolateral pain was 6 years. At the time of surgery the main complaint was retromalleolar pain in nine patients, pain and instability in eight patients, and instability only in one patient. Diagnosis of tendinous lesions was based on clinical examination in three cases, preoperative magnetic resonance imaging in eight cases, preoperative tenography in one case, and surgical exploration in six cases. The lesion was localized at the tip of the lateral malleolus and was visible only after opening the peroneal retinaculum. In three cases an accessory peroneal muscle was present. A Chrisman-Snook procedure was performed in 13 cases and a simple tendinous repair in 5 cases. The split lesion of the peroneus brevis tendon may be the result of chronic ankle laxity. This lesion needs a specific surgical treatment and the peroneal tendon must be checked in case of surgical procedure for ankle laxity. After ligamentous repair, residual pain can be due to a neglected peroneus brevis tear.