This paper discusses the long-term results of the anterior cruciate ligament (ACL) reconstruction with the Leeds-Keio (LK) prosthetic ligament. For this type of reconstruction we used arthrotomy and an arthroscopy-assisted technique. The fixation was obtained with two bone plugs, and the distal portion was also attached with a staple. A postoperative protocol was used with a progressive range of motion and weight bearing after 50 days. We performed 50 LK operations in professional and amateur athletes aged 17-39 years with an isolated anterior instability. We reviewed at follow-up (5-7 years) 37 patients; 8 were lost, and 5 had a subsequent failure. At the Lysholm score the patients were classified: 19 excellent, 13 good, 3 fair, and 2 poor. At the IKDC grading the patients were classified as follows: 2 class A, 22 B, 8 C, and 5 D. The Lachmann test was 1+ in 15 patients, 2+ in 7, 3+ in 2, and negative in 13; pivot shift was 1+ in 9, 2+ in 7, 3+ in 2, and negative in 25. Results of the KT 1000 test at 30 lb side to side was < 3 mm in 23 patients, 3-5 mm in 6, 6-10 mm in 6, and > 10 mm in 2. In view of the results observed and the progressive deterioration over the years, this procedure should no longer be performed as an ACL substitute.