To evaluate the effect of tourniquet use during anterior cruciate ligament reconstruction, 40 consecutive patients were randomized into two groups: Group I (tourniquet) and Group II (no tourniquet). Preoperative evaluation included electromyography, measurement of thigh and calf girth, and determination of serum creatinine phosphokinase levels. Initial postoperative evaluations included serial creatinine phosphokinase determinations. At 1 and 6 months postoperatively, the electromyographic examination was repeated and thigh and calf girth measurements were obtained. At 6 months and 1 year after surgery, the following evaluations were made: thigh and calf girth, KT-1000 arthrometric testing, isokinetic testing of quadriceps and hamstring muscles, single-legged hop test for time, single-legged hop test for distance, and the Lysholm knee score. In Group I, the tourniquet was inflated for an average of 87 minutes, with an average pressure of 269 mm Hg. At 1 month postoperatively, 6 of 20 patients in Group I had positive electromyographic recordings (compared with 2 of 20 in Group II, P = 0.08). At 1 month, thigh girths measured 10 cm proximal to the medial joint line suggested more atrophy in the tourniquet group (P = 0.07). At 6 months, all electromyographic recordings had returned to normal. At 6 months and 1 year postoperatively, girth measurements, isokinetic strength testing, functional testing, KT-1000 arthrometer evaluation, and the Lysholm knee scores were similar for both groups.