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Incidence is estimated at between 1 in 100,000 and 2 in 100,000.

Precise definitions of the diagnostic criteria for the different types of JIA were established in 2001 at the last international meeting in Edmonton. Six disorders have been defined: systemic-onset juvenile idiopathic arthritis (formerly referred to as Still's disease), oligoarticular arthritis, rheumatoid factor-positive polyarthritis, rheumatoid factor-negative polyarthritis, enthesitis-related arthritis (spondylarthropathies), and the juvenile form of psoriatic arthritis (see these terms). A seventh category has been defined comprising unclassified types of arthritis (types that do not correspond to any of the defined disease or that correspond to more than one of the disease definitions).

The criteria that define the diseases are mainly clinical, but genetic studies (in particular linkage with HLA antigens) confirm that these are different disorders and not different clinical forms of a single disease.

Treatment of JIA is best managed in specialised centres where rheumatologists and paediatricians work in collaboration with physiotherapists, paediatric orthopaedists and psychologists to ensure global management of the medical aspects of the disease and its consequences on school and family life. Since 2000, biotherapeutic approaches targeting inflammatory cytokines, such as the tumour necrosis factor (TNF)-alpha inhibitor Etanercept, have revolutionised the management and prognosis of severe forms of the disease. Methotrexate remains the second-line treatment of choice. However, results with methotrexate and anti-TNF-alpha agents in patients with systemic forms of the disease have been disappointing. For these patients, several other treatments are available and/or under investigation such as thalidomide, an interleukin-1 receptor antagonist (anakinra), and the anti-interleukin-6 receptor (IL-6R) monoclonal antibody (MRA). Given this range of treatment options, it is very important to provide early specialised care so that treatment can be adapted to each child. In addition, there is also a risk of uveitis, which may evolve without symptoms or eye redness but may have severe consequences in the absence of early treatment. Thus, regular ophthalmologic monitoring, including slit-lamp examination of the eyes, should be performed every three months for young children with oligoarticular arthritis or rheumatoid factor-negative polyarthritis.