An unstable knee presents a real challenge to the orthopaedic surgern in view of the treatment. However, currently, as more and more of our citizens participate in the recreational activities that expose the always vulnerable knee joint to undue stress, and victims who are injured by traffic accident are increased. Orthopaedic surgeons are seeing more and more people who have knee instability severe enough to prevent them from participating in sports, in labor, and in the many other activities which may stress their knees. 95 patients suffering from ligamentous injuries of the knee have been treated by operation at Inje Medical College Paik Hospital from June 1, 1979 to February 28, 1983. 57 of the 95 patients with a minimum follow up of 6 months returned for evaluation. 1. Through the follow up study, we can obtain following results. 25 of 29 cases (86.2%), operated upon within 2 weeks of the time of injury, were good or fair(+), and 7 of 20 cases (35.0%), operated upon between 2 weeks and 3 months of the time of injury, were good or fair (−). 2. The most significant fact is that the result of 16 of 18 cases(88.9%), operated upon the anterior cruciate ligament, were good and excellent or fair(+), and 8 cases, operated upon posterior cruciate ligament, were all good and excellent or fair(+). 3. Cruciate ligament reconstruction using central one-third of the patellar ligament is more effective procedure for achieving static and functional stability of the knee than any others.