Between 1977 and 1985, 170 patients suffering from chronic Achilles tendinitis were treated surgically. Ninety-one patients with 143 tendons returned for followup. The duration of preoperative symptoms averaged 18 months. In all cases, conservative treatment was first attempted but failed to alleviate symptoms. Only those patients whose lesions and symptoms were confined to the Achilles tendon segment 2 to 6 cm proximal of the insertion were included in this study. All athletes who had an insertion tendinopathy or a lesion at the musculotendinous junction were excluded from this study. The surgical procedure depended on the lesion. For 93 tendons exhibiting pure peritendinitis, treatment consisted of a simple release of the fascia cruris and the peritenon. For the 50 tendons with tendinosis, a resection of diseased tendon tissue was performed. The defect could be sutured side to side in 26 cases but in the other 24 cases, reinforcement with a turned down tendon flap was necessary because of the extensive debridement. Of the 93 cases in which only dorsal release was performed, results were considered excellent in 54 cases, good in 28, fair in 8, and poor in 3 cases. Of the 26 cases in which side-to-side suture was performed, 15 cases were rated as having excellent results, 4 as good, 4 as fair, and 3 as poor. For the 24 cases in which a turned down tendon flap procedure was performed, the result was excellent in 12 cases, good in 9, fair in 2, and poor in 1 case.(ABSTRACT TRUNCATED AT 250 WORDS)