The results of reconstruction of the anterior cruciate ligament with the central third of the patellar ligament as a free, autogenous, non-vascularized graft were retrospectively reviewed at our institution. Eighty reconstructions in seventy-nine patients were evaluated after a minimum of two years. In forty-eight (60 per cent) of the knees, the reconstruction was augmented with an extra-articular lateral sling of iliotibial band. The patients were evaluated with a physical examination, a KT-1000 arthrometer, radiographs, a subjective questionnaire, and a revision of the scale of The Hospital for Special Surgery for rating ligaments. Postoperatively, seventy-six (95 per cent) of the eighty knees no longer gave way, and the pivot-shift test was negative in sixty-seven (84 per cent) of the knees. The average score on the ligament-rating scale was 93 points. All of the patients who had clinical instability at the time of the most recent follow-up had associated ligamentous instability that had not been appreciated or addressed at the time of reconstruction. Arthrometric evaluation revealed that the laxity differed by three millimeters or less from that of the untreated knee in sixty (76 per cent) of the treated knees. In the patient who had bilateral reconstruction, the laxity was the same in both knees. Seventeen patients, who had more than three millimeters of translation, also had additional related ligamentous instability, most commonly posterolateral instability and insufficiency of the medial collateral ligament. We think that major associated ligamentous instability predisposes the reconstruction to failure and should be corrected in conjunction with the reconstruction.(ABSTRACT TRUNCATED AT 250 WORDS)