Nine patients with rheumatoid arthritis, who had Silastic prostheses (Swanson's) introduced into 34 metacarpophalangeal joints, were reviewed 5 years after surgery. The most important long-term advantage conferred by the introduction of prostheses was pain relief; functional benefit was marginal. The majority of prostheses eventually fractured but this did not necessarily lead to a functional deterioration. Impairment of function was usually the result of loss of flexion at the metacarpophalangeal joints, but it was sometimes due to excessive instability after fracture of the prostheses. It is suggested that Silastic joint replacement may be a worthwhile procedure in rheumatoid patients with moderate destruction or deformity of the metacarpophalangeal joints when pain is a predominant feature. Significant functional improvement can be anticipated only when secondary to pain relief.