The authors have treated 52 cases of septic arthritis of major joints. When aspiration contain an opaque fluid, conservative treatment with antibiotic therapy and immobilisation obtained healing in half of the patients. Surgical lavage of the joint was needed on 21 occasions with healing in 15. Synovectomy was performed in 8 cases and was indicated only at the stage of pyogenic synovitis before the development of pyogenic arthritis. When the latter stage was reached, arthrodesis was indicated. It was performed primarily on 6 occasions and secondarily once. Seven patients died. The average age was seventy years. The importance of early treatment is stressed.