A follow-up study was made of 26 knees of 21 patients who underwent arthroscopic synovectomy between October 1982 and August 1983 in Catholic Medical College and Center. The patient's ages ranged from 3 to 66 years of age. There were 14 female patients and 7 male patients in this series. The follow-up period of all patients was a minimum of twelve months to a maximum of 20 months. The average follow-up of the whole group was 16.8 months. The abnormal findings were rated from 0 to 4 according to Marmors rating system. Final clinical evaluations of the patients were done according to the modified criteria of Sledge et al. The results were as follows; 1. Rheumatoid Arthritis Of 14 knees, 3 joints(21.4%) were rated “excellent”, 6(42.9%) were “good”, and 5(35.7%) were “fair”. There was no case of “unimproved”. 2. Juvenile Rheumatoid Arthritis The results of all 5 knees were satisfactory. Of 5 knees, 4 joints(80%) were rated excellent and one joint (20%) was good. 3. There were 3 knees of osteoarthritis, 3 knees of chronic synovitis and one knee of pigmented villonodular synovitis. Their final results were all satisfactory. Three joints were rated excellent and the other 3 joints were good. 4. Of 26 knees, as a whole, 10 joints (38.5%) were rated “excellent”, 11 joints (42.3%) were “good”, 5 joints (19.2%) were “fair” and no joint was “unimproved”. There were 5 recurrences of active synovial disease in this series, and these patients all were “classic” rheumatoid arthritis. But surprisingly the average patient in this group of recurrence did well even after recurrence. These patients all had less pain and effusion than before operation. 5. The major cause of unsatisfactory results other than recurrence of synovitis were articular degeneration (joint space narrowing) and patellofemoral osteoarthritis (4 knees). 6. A good range of motion with the shortest rehabilitation period can be expected if alternate flexion and extension splints are applied on alternate days for less than a week following the surgery. In conclusion, one may state that the arthroscopic synovectomy is worth considering for the treatment of various kinds of synovitis of the knee joint and when the rheumatoid process follows a favourahle course.