Purpose: We reviewed the value of treatment for chronic lateral instability of theankle with arthroscopic procedure combined with Brostrom one. Material and Method: From May 2000 to June 2002, 18 patient with chronic lateral instability of the ankle with Modified Brostrom procedure and arthroscopic one. Mean follow-up period was 18 months. Result: Chronic lateral instability of the ankle almost had intraarticular pathology, such as osteophye, osteochondral lesion, So we could resolve intraarticular pathology by arthroscopic procedure during Brostrom one for lateral collateral ligament reconstruction. Conclusion: Modified Brostrom procedure and arthroscopic one are an excellent treating method for chronic lateral instability of the ankle which has intraarticular pathology.