Objective. To describe the long-term outcome and determine predictors of severity among patients with oligoarticular-onset juvenile idiopathic arthritis (JIA).Methods. In a longitudinal study, 207 patients with oligoarticular-onset JIA who were referred between 1988 and 1998 were evaluated. At disease onset, selected clinical and laboratory data were collected as independent variables. A polyarticular disease course, joint erosion, uveitis, and remission were assessed as dependent variables. Longitudinal analyses were performed with the Kaplan-Meier method, and multivariate analysis with the Cox model.Results. After 6 years of followup, the probability of a polyarticular course of disease was 50%, joint erosion was 35%, uveitis was 30%, and remission was 23% in these patients. Joint erosion was strongly associated with a polyarticular course. A high erythrocyte sedimentation rate (ESR) as well as involvement of more than 1 joint or involvement of an upper limb at disease onset were predictors of disease extension. A high ESR was also a strong predictor of a destructive course, and a family history of psoriasis was predictive of uveitis occurrence. No predictive factor for remission could be identified.Conclusion. Oligoarticular-onset JIA is a severe disease with frequent complications. Factors predictive of severity in oligoarticular-onset JIA were identified. This could allow early identification of high-risk patient subgroups, warranting a more aggressive therapeutic approach.