The objective of this study was to compare the patellar tendon tibial shaft angle at specific angles of knee flexion in young male and female athletes with lower extremity weight-bearing to determine if a gender difference exists. Twenty healthy recreational athletes (10 males and 10 females) aged 22 to 28 years with normal knees were recruited. Seven lateral radiographs of each subject's dominant knee were obtained at knee flexion angles of 0°, 15°, 30°, 45° 60°, 75° and 90°. Measurements from the radiographs were used in a multiple regression analysis to express the patellar tendon tibial shaft angle as a function of knee flexion angle. Our results indicate that the patellar tendon tibial shaft angle is a linear function of knee flexion. Female subjects' average patellar tendon tibial shaft angle was 3.7° greater than male subjects'average patellar tendon tibial shaft angle (p = 0. 00). The gender differences in patellar tendon tibial shaft angle results in a 13.2% increase in the anterior shear force applied to the tibia of the average female subject, compared to the average male. These results indicate that patellar tendon tibial shaft angle may be an anatomical risk factor for noncontact anterior cruciate ligament injuries, especially in female athletes.