In brief: The anterior cruciate ligament is the most often seriously injured knee ligament. Because effusion and muscle guarding often accompany ACL injury, immediate field examination is advised. Several traditional tests such as the anterior drawer test and the Lachman test can be used to check the integrity of the ACL. Each has strengths and weaknesses with regard to diagnostic value and ease of use, all of which should enter into decisions about their appropriateness in ACL injuries. In addition, the author has devised a test—the femur stabilization test—to provide insight into the ACL evaluation process.