Immediate weightbearing has been advocated after anterior cruciate ligament reconstruction and is thought to enhance the return of quadriceps muscle activity and knee extension range of motion without jeopardizing graft integrity. This study examined the effect of immediate weightbearing after anterior cruciate ligament reconstruction on the return of vastus medialis oblique electromyography activity, knee extension range of motion, knee stability, physical examination, Lysholm score, and anterior knee pain. Forty-nine patients (24 men and 25 women) undergoing endoscopic central third patella tendon autograft reconstruction were randomized prospectively into two groups. Group 1 patients underwent immediate weightbearing as tolerated. Group 2 patients were kept nonweightbearing for 2 weeks. All measurements were taken before surgery, 2 weeks after surgery, and between 6 and 14 months (average, 7.3 months) followup. There was no effect of weightbearing on knee extension range of motion or vastus medialis oblique function at followup. In addition, knee stability was not compromised after surgery. Seven of 20 (35%) nonweightbearing patients and only two of 25 (8%) immediate weightbearing patients reported anterior knee pain at followup. Overall, immediate weightbearing did not compromise knee joint stability and resulted in a better outcome with a decreased incidence of anterior knee pain.