Ross River virus is a mosquito-transmitted alphavirus indigenous to Australia, Papua New Guinea and nearby islands, which recently appeared in other western and central South Pacific islands. Human infection can be manifest by varied constitutional disturbances, rash and rheumatic symptoms, known in Australia as epidemic polyarthritis and broadly similar to certain alphavirus diseases in other regions. Although usually short-lived, the rash can persist for 5 months. Rheumatic effects involve synovial joints, tendon and ligaments, and can continue or recur in peripheral joints and tissues as long as 6 years, though gradually improving without destructive changes. At different times, the disease can closely simulate rubella and other virus diseases, Henoch-Schönlein syndrome, rheumatoid and other chronic rheumatic diseases. Diagnosis rests upon geography, specific serology and judicious interpretation of clinical and supportive laboratory data. Skin and synovial lesions are characterized by infiltration of mononuclear cells. Their pathogenesis most likely depends on the reaction of these cells with persistent foci of virus disseminated during the early viraemic phase of infection.