Similarities and differences between systemic juvenile idiopathic arthritis and adult-onset Still's disease: a multicenter Spanish study.

To describe the characteristics of systemic juvenile idiopathic arthritis (sJIA) and adult-onset Still's disease (AOSD), compare their presentation and evolution, and analyse possible complication predictors. Multicenter study. Data were retrieved from a hospital-based study of patients with a diagnosis or suspected diagnosis of sJIA or AOSD according to the responsible physician and followed-up for at least one year.