There are an estimated 80,000 to 100,000 anterior cruciate ligament (ACL) repairs in the United States each year. Most ACL tears occur from noncontact injuries. Women experience ACL tears up to nine times more often than men. Evaluation of the ACL should be performed immediately after an injury if possible, but is often limited by swelling and pain. When performed properly, a complete knee examination is more than 80 percent sensitive for an ACL injury. The Lachman test is the most accurate test for detecting an ACL tear. Magnetic resonance imaging is the primary study used to diagnose ACL injury in the United States. It can also identify concomitant meniscal injury, collateral ligament tear, and bone contusions. Treatment consists of conservative management or surgical intervention, with the latter being the better option for patients who want to return to a high level of activity. Patients who undergo surgery must commit to appropriate rehabilitation for the best outcome. Long-term sequelae of ACL injury include knee osteoarthritis in up to 90 percent of patients. Primary prevention of ACL injury includes specific proprioceptive and neuromuscular training exercises to improve knee stability.