Septic arthritis of the hip and knee is very common in children and adolescents. Sixteen consecutive patients were treated for septic arthritis of the kee with arthroscopic lavage and debridement. Ten of the 16 knees were culture positive on preoperative aspiration. The average duration of antibiotic treatment was 19 days. The mean immobilization period was 1 1/2 days and the time to full and painless range of motion averaged 2.8 weeks. All patients resumed normal activities by 3 weeks, no infections recurred, and postoperative morbidity was minimal.