We performed a prospective study of 46 patients with ruptures of the anterior cruciate ligament and medial ligamentous structures. All patients had anterior cruciate ligament allograft reconstructions. Group I comprised 34 patients in whom all of the medial structures were ruptured (parallel and oblique fibers of the superficial medial collateral ligament and the posteromedial capsule) and were treated operatively. In Group II (12 patients), the superficial medial ligament fibers only were ruptured and these were treated nonoperatively. All patients started an immediate motion and rehabilitation program. Forty-four patients returned for followup at a mean of 5.3 years (range, 2 to 8.9) postoperatively. The results were assessed using the Cincinnati Knee Rating System. At followup, 20 knees (59%) in Group I and 9 knees (73%) in Group II had less than 3 mm of increased displacement on KT-1000 arthrometer testing (134 N). The overall rate of anterior cruciate ligament graft failure was 15%: six (18%) in Group I and one (8%) in Group II. No patient had more than 2 mm of increase on valgus stress testing at 5 degrees or 25 degrees of knee flexion. The overall ratings were as follows: Group I, 20 knees (58%) excellent or good and 14 knees (42%) fair or poor; and Group II, 11 knees (91%) excellent or good and one knee (9%) fair. Knee motion complications and patellofemoral symptoms were common in the patients rated fair or poor in Group I.