A follow-up study of 56 patients with the provisional diagnosis of polymyalgia rheumatica showed that 12 developed peripheral synovitis during the course of the illness. Five of the 12 were noted to have synovitis on presentation which was characteristically mild, pauci-articular and cleared quickly after commencing prednisolone therapy. The remaining seven had persistent synovitis of peripheral small joints despite an initial brisk response to oral prednisolone. Five of these patients were found to satisfy the ARA criteria for rheumatoid arthritis after a mean follow-up period of 3.5 years. It is suggested that the persistence of peripheral synovitis in patients treated as polymyalgia rheumatica should alert the clinician to the possible development of rheumatoid arthritis.