This study was undertaken to evaluate the efficacy of knee synovectomy with arthroscopic technique. Nineteen patients with 25 operated knees were studied. All 25 knees had 6-month follow-up, 21 knees had 2-year follow-up, and 14 knees were evaluated at least 4 years after operation. After operation, patients were evaluated using clinical data including pain relief, functional capacity, range of motion, recurrent synovitis, and presence of effusion. Preoperative as well as follow-up weight-bearing radiographs were also studied to assess the results of this procedure. At 6 months' postoperative clinical evaluation, 96% of patients showed good results. At 2 years, 90% of patients were considered to have good results, and at 4 years, 57% of patients continued to do well. Of those knees studied radiographically, 81% showed no progressive radiographic changes at 2 years and 61.5% showed no deterioration at 4 years. Clinical results correlated well with radiographic results. Arthroscopic synovectomy yielded results similar to those previously published for open synovectomy, with less operative and postoperative morbidity.