Anterior cruciate ligament (ACL) injuries are common, especially in young individuals who participate in sports activities associated with pivoting, decelerating and jumping. About 70% of ACL injuries do not result from direct contact. Establishing risk factors is important for prevention strategies. Risk factors for ACL injuries include environmental factors (e.g. high level of friction between shoes and the playing surface) and anatomical factors (e.g. narrow femoral intercondylar notch and increased joint laxity). History taking and physical examination provide the basis for diagnosis. Magnetic resonance imaging (MRI) is highly sensitive and specific and provides information about associated injuries such as meniscal tears. ACL-injury leads to knee instability which is associated with both acute dysfunction and long-term degenerative changes, such as osteoarthritis and meniscal damage. Surgical treatment of ACL-tears is effective in regard to short term rehabilitation but does not necessarily alter the natural course of this injury and its long-term complications. Therefore, surgical treatment should be reserved primarily for young individuals and for those who are high risk for ACL injury. ACL reconstruction is the standard surgery; however, a wide variety of reconstruction procedures is available and a gold standard procedure has not been defined. Nevertheless, arthroscopic reconstruction with either bone-patellar tendon-bone or a hamstring tendon graft is the most widely used method. Surgical timing is important. Early surgical intervention (i.e. within 4 weeks of injury) might increase complications.