Reconstructjon of old anterior cruciate ligament injury was divided into extraarticular and intraarticular group. The intraarticular ligament reconstruction was a reliable method to correct the rotational axis of knee joint instability. Authors studied 10 cases in 10 patients who were treated by reconstruction of anterior cruciate ligament using patellar tendon under arthroscopy from January, 1988 to June, 1989. The follow up period was over 10 months. 7 cases were negative in Lachman test and 2 cases had mild instability of knee joint. The postoperative result was excellent in 3 cases, good in 4 cases, fair in 1 case, and failure in 1 case according to Clancy's evaluation. We concluded that the reconstruction of anterior cruciate ligament injury using patellar tendon under arthroscopy was an effective method in the treatment of old anterior knee instability.