Tension in an anterior cruciate ligament graft is greater with the knee in flexion when the angle of the tibial tunnel in the coronal plane is vertical or more perpendicular to the medial joint line of the tibia; however, the relationship of the angle of the tibial tunnel to knee function has not been studied. Greater graft tension may limit knee flexion or stretch the graft and increase anterior laxity. Five surgeons treated 119 subjects by reconstructing a torn anterior cruciate ligament using a double-looped semitendinosus and gracilis graft and a standardized technique. The femoral tunnel was drilled through the tibial tunnel. Radiographs were analyzed for tibial tunnel placement and a clinical evaluation was made 4 months postoperatively. Knees were assigned to subgroups according to the angle of the tibial tunnel in the coronal plane (65 degrees to 69 degrees, 70 degrees to 74 degrees, 75 degrees to 79 degrees, 80 degrees to 84 degrees, and 85 degrees to 89 degrees), with the angle of the latter subgroup being most vertical. Loss of flexion increased significantly from 0.5 degrees to 6.5 degrees and anterior laxity increased significantly from 0.5 to 2.2 mm as the tunnel angle was increased. The average angle of the tibial tunnel varied significantly, 11 degrees between surgeons (range, 69 degrees to 80 degrees). We found a tibial tunnel angle of 75 degrees or more is associated with greater loss of flexion and anterior laxity. Surgeons do not drill the angle of the tibial tunnel in the coronal plane accurately. We now routinely drill the tibial tunnel at an angle of 65 degrees to 70 degrees in the coronal plane because it may reduce loss of flexion and anterior laxity.