The cases histories of 51 rheumatoid arthritis patients (58 hands) were examined retrospectively with respect to the incidence of tendon rupture. Factors that were associated with tendon rupture such as X-ray changes in the wrist joint and clinical findings of the hand preceding the tendon rupture were statistically analysed. In a separate study, prophylactic tenosynovectomy and wrist synovectomy were performed on 42 joints in 35 patients who had two or more risk factors. This group of patients was then analysed for subsequent tendon rupture and recurrent synovitis. The risk factors for the extensor tendon rupture in the dorsal wrist joint were found to be: dorsal dislocation of the distal ulna; a scallop sign on X-ray; and tenosynovitis persisting for at least 6 months. Prophylactic surgery effectively prevented rupture of the tendons in patients who had two or more risk factors for extensor tendon rupture.