We reviewed the long-term natural history of 21 adult-onset Still's disease patients. Patient subsets were identified according to clinical course patterns. These included monocyclic systemic disease in 4, polycyclic systemic disease in 2, chronic articular monocyclic systemic disease in 10, and chronic articular polycyclic systemic disease in the remaining 5 patients. Functional outcome differed according to course patterns and the extent of articular involvement. Systemic manifestations, per se, did not contribute to poor functional prognosis. Chronic articular disease had the worst outcome: 27% evolved to functional class III status, compared with none in the cyclic systemic groups. Those patients who had a chronic articular pattern or a polyarticular onset and course were at higher risk to develop disabling arthritis. An aggressive approach to therapy, including the early use of remittive agents, should be considered in these patient subsets.