The study involves a group of patients affected with inveterate lesion of the A.C.L. for at least 18 months. Homogeneous two-staged surgical treatment was carried out: 1) reconstruction of the A.C.L. according to Kenneth-Jones; 2) retention of the popliteus according to Bousquet. Results were: excellent: 18; good: 10; fair: 2. Follow-up was obtained after an average of 18 months.