Changes can occur in the peroneus brevis tendon following ankle injuries or sprains. A series of 14 tendon lesions is reported in the ankles of 13 patients. The duration of symptoms ranged from 8 months to 20 years. The predominant symptom in 12 ankles was lateral pain. In 11 ankles, lateral ankle instability was treated by a reconstruction with the split peroneus brevis graft, and in one ankle, by direct repair. The defects were found during harvest of the graft. One patient had previous fractures with bony impingement and one had a chronic tear of the tibialis posterior tendon with pes planus. All lesions were located in the segment of the tendon at or distal to the lateral malleolus. The lesions were 2 to 5 cm in length, single or multiple, and with a grossly degenerative appearance. No avulsions or anomalies of the tendon were found. In 11 patients, the defect in the peroneus brevis was incorporated into the portion of the tendon in ankle ligament reconstruction for use as a graft; in 2 cases it was repaired directly. On follow-up of eight months to four and one half years, twelve ankles had significant improvement in pain and function.