A prospective study was done of the use of allogeneic tissue to reconstruct the anterior cruciate ligament in knees in which an intra-articular or an extra-articular operation had failed. Sixty-six consecutive patients (sixty-six knees) had such an operation with use of bone-patellar ligament-bone allografts; all but one returned for follow-up evaluation twenty-three to seventy-eight months (mean, forty-two months) after the operation. A total of 235 previous operations had been performed in these sixty-six knees, including eighty-one procedures for rupture of the anterior cruciate ligament. The results of the allograft procedure were evaluated with a subjective and objective system that rated twenty factors. The anterior-posterior displacement was substantially improved in most of the patients. According to data derived from arthrometric studies and pivot-shift tests of the fifty-seven patients who were so evaluated and in whom the condition was unilateral, 53 per cent (thirty) of the reconstructed ligaments were determined to be functional; 21 per cent (twelve ligaments), partially functional; and 26 per cent (fifteen ligaments), a failure. When we calculated the rate of failure by including ten failures that had occurred within two years after the operation with the fifteen that occurred in patients who had been followed for at least two years, the over-all rate of failure was 33 per cent (twenty-five of seventy-five operations). There was significant improvement in the subjective ratings of functional limitations and symptoms (p < 0.01) and in the over-all rating score (p < 0.0001). However, there was a significant difference between the scores of the patients in whom the surfaces of the articular cartilage had appeared normal at the index operation and those of the patients in whom there had been noteworthy fissuring and fragmentation or exposure of subchondral bone. After the program of rehabilitation, which included immediate motion of the knee, a range of motion of 0 to 135 degrees was restored in all but five knees, four of which lacked only 5 degrees of this extent of flexion or extension. The results demonstrate that bone-patellar ligament-bone allografts may be used when proper autogenous tissues are not available and that symptoms and abnormal displacement were reduced in most of our patients.