One hundred and eleven consecutive patients who had acute injuries to the knee that included rupture of the anterior cruciate ligament, as shown by physical examination with the patient under anesthesia and by diagnostic arthroscopy, were randomized to three treatment groups: simple repair of all injured structures, repair of all injured structures and augmentation of the anterior cruciate ligament with a strip of the iliotibial band, and repair of all injured structures except the anterior cruciate ligament. In all other respects, the knees were treated in an identical fashion. Of the 111 patients, 107 were re-examined forty-five months or more after operation. At the most recent follow-up, the knees that had been treated by repair and augmentation of the anterior cruciate ligament were significantly more stable and had had significantly fewer subsequent meniscal tears. Sufficient instability to necessitate late reconstruction was also less frequent in the patients who had had an augmented repair. These patients had better function of the knee and a higher level of activity than the patients in the other two groups. Sixty-four per cent of these patients who had a rupture of the anterior cruciate also had a meniscal tear, and primary care was indicated for more than 50 per cent of the tears. Therefore, we believe that early arthroscopic examination is essential for patients who have an acute rupture of the anterior cruciate ligament.