Juvenile idiopathic arthritis (JIA), formerly know as juvenile chronic arthritis, is a broad term encompassing several disorders starting before the age of 16. It is characterized by arthritis lasting more than 6 weeks, of unknown etiology, usually persisting for six month initially. Approximately 1 in 5 000 children are affected in France. Of the various distinguishable clinical forms, oligoarticular JIA is the most frequent one. It is characterized by an involvement of up to 4 joints during the first 6 months and is mostly observed in females. The prognosis may be further complicated by the presence of uveitis, associated with an insidious progression. In systemic JIA (also called Still's disease) as well as in some polyarticular forms, with or without rheumatoid factor, inflammation may continue in adulthood. Severe polyarticular involvement or hip involvement may be associated with a poor functional prognosis.