The anterior cruciate (ACL) is the most frequently ruptured ligament of the knee. Some authors have suggested that excessive internal tibial rotation concomitant with hyperpronation of the subtalar joint during stance and inherent knee joint laxity may predispose an athlete to knee injury. Over a period of 2 years, we identified 14 ACL-injured football players and eight ACL-injured female basketball players and gymnasts. We matched them by sport, team, position, and level of competition with 22 athletes without history of ACL injury. Measures of navicular drop, calcaneal alignment, and anterior knee joint laxity with a KT-1000 were obtained from the uninjured knee of the ACL-injured athletes and compared with measures obtained from the ACL-noninjured athletes. ACL-injured athletes had greater amounts of navicular drop, suggesting greater subtalar pronation and greater anterior knee joint laxity. Discriminant analysis and multiple regression indicated that these variables correctly predicted injury status for 87.5% of the females and for 70.5% of all cases. These results suggest that the more an athlete pronates and the greater the anterior knee joint laxity, the greater the association with ACL injury.