Anterior cruciate ligament (ACL) injuries are increasingly common in the United States. This may be related to the increase in high school sports participation, particularly in female athletes. A significant proportion of these injuries are caused by noncontact mechanisms. The incidence of these noncontact injuries may be significantly reduced by enrolling young athletes in jump-training programs. The diagnosis of ACL injuries involves a focused history and physical examination, which can provide a high index of suspicion. Although radiographs are important to rule out associated injuries, the gold standard for diagnosis of ACL injuries is MRI, which has shown excellent accuracy.