The anterior cruciate ligament injury is one of the most common ligament injury of the knee joint, and anterior cruciate ligament is as important structure for stabilization as a primary restraint. Noyes reported that the diagnosis of a tek of the anterior cruciate ligament was made by the original treating physician in only 6.8%. And there are many controversies in its treatment. It is certain thatearly diagnosis and treatment are th most important clue. Authors studied 48 patients of isolated anterior cruciate ligament injury who were diagnosed by same physician from Jan. 1983 to Dec. 1985 after follow ups ranging from six mnths to 4 years, average beimng one year and two months. The results were as followings: 1. The most common cause was sports injury. 2. The most common sign and symptom were hemarthrosis in acute injury and giving way in chronic injury. 3. Anterior drawer test without anesthesia had 25% of diagnostic accuracy but pivot shift test under anesthesia 95.8%. 4. 31 cases in 48 cases (64.8) had associated meniscal injury. 5. In acute torn ACL, the primajy repair was preparable but conservative treatment with arthroscopic partial menisectomy was eful in chronic case.