Progress in achieving international consensus concerning the classification of juvenile idiopathic arthritis has been made, although further refinement and validation of these criteria is needed. It is hoped that this will facilitate more effective international collaboration in the study of these diseases, because much remains to be learned about genetic susceptibility, causation, pathogenesis, and treatment. Attention to the unique aspects of chronic arthritis in children such as impaired growth and macrophage activation syndrome may help to reduce disease-related morbidity and mortality. New biologic agents have substantially enhanced the treatment of JRA. The identification of reliable predictors of disease course and outcome is important in the rational and timely application of new therapies.