A study was performed on the effect of the addition of an extra-articular procedure involving tenodesis of the iliotibial band to a reconstruction with a bone-patellar ligament-bone allograft for the treatment of chronic rupture of the anterior cruciate ligament. One hundred and four patients were divided into two groups for comparison: Group 1 (sixty-four patients) was treated with only an intra-articular replacement with an allograft and Group 2 (forty patients), with both an intra-articular replacement with an allograft and the extra-articular procedure. Preoperatively, there were no statistically significant differences between the two groups in terms of twenty variables, including body weight, level of activity, anterior-posterior displacements, number of previous operations, and duration of follow-up. All of the patients returned for follow-up evaluation twenty-three to fifty-four months (mean, thirty-five months) postoperatively. All were treated with the same postoperative program of immediate motion of the knee and rehabilitation. The results were evaluated with the use of a comprehensive subjective and objective system that rated the twenty factors. Both procedures proved to be effective in decreasing functional limitations and symptoms and in improving the level of sports activity and the over-all scores. The results in Group 2 were significantly better than those in Group 1, as measured with tests done with the KT-1000 arthrometer (p less than 0.01) and with regard to the level of sports activity (p less than 0.05) and the over-all scores (p less than 0.01). There was no postoperative difference between the two groups in terms of the results on pivot-shift or isokinetic testing, patellofemoral crepitus, functional limitations, or symptoms. The program of rehabilitation effectively restored 0 to 135 degrees of motion to all but four knees, which lacked 5 degrees of extension at the most recent follow-up. The over-all rate of failure for both groups was 11 per cent. However, the rate of failure was 16 per cent (ten of sixty-four knees) in Group 1 and only 3 per cent (one of forty knees) in Group 2. This difference was significant (p less than 0.05). The extra-articular procedure appeared to provide support to the healing intra-articular allograft by reducing deleterious forces and tibial displacements, and to restore the secondary restraints provided by the lateral iliotibial band. The results suggest that the combination of the procedures is of value in young, athletically active people who have chronic rupture of the anterior cruciate ligament.(ABSTRACT TRUNCATED AT 400 WORDS)