A five-year, prospective, randomized follow-up study was done to compare three methods for repair of a rupture of the anterior cruciate ligament of the knee: acute primary repair (Group 1), acute repair with a synthetic ligament-augmentation device (Group 2), and acute repair augmented with an autologous bone-patellar ligament-bone graft (Group 3). One hundred and fifty patients who had an acute rupture of the anterior cruciate ligament were randomized to one of the three repair groups, with fifty patients in each group. The patients were between sixteen and fifty years old (mean, twenty-nine years old). All patients had the operation within ten days after the injury. The rehabilitation protocol was identical for each group. The patients were evaluated prospectively at one, two, and five years with use of the Tegner scoring system for level of activity and the scoring system of Lysholm and Gillquist for function, and the stability of the knee was assessed with clinical examination and with use of the KT-1000 arthrometer. One hundred and thirty-one patients completed the study and ten other patients were known to have had a failure of the procedure, a 94 per cent rate of follow-up.All three groups had a lower level of activity at the five-year follow-up evaluation than they had had before the injury. The patients who had had augmentation with a patellar-ligament graft had a significantly higher mean level of activity at two years than those who had had non-augmented repair (p = 0.002) and those who had had repair with a synthetic ligament-augmentation device (p = 0.01). They also had a significantly higher mean level of function at two years than those who had had non-augmented repair (p = 0.0001) and those who had had repair with a synthetic ligament-augmentation device (p = 0.03) and a significantly higher mean level of function at five years than those who had had non-augmented repair (p = 0.004). The ability to attain full extension improved significantly in all three groups during the five-year follow-up period; the highest gains occurred in the group that had had augmentation with a patellar-ligament graft.Rotatory and anterior instability progressively increased during the follow-up period for all three groups. At one, two, and five years, the knees that had had repair with a patellar-ligament graft were significantly more stable than those that had had non-augmented repair and those that had had repair with a ligament-augmentation device (p < 0.0001 to p = 0.03).The findings of this study reinforce the conclusions of our two-year follow-up report that a non-augmented primary repair should not be performed, a repair with a ligament-augmentation device has an unacceptably high rate of failure (more than one-third of the patients), and a repair that is augmented with the patellar ligament has the best outcome.