Development of diagnostic criteria for juvenile rheumatoid arthritis, systemic lupus erythematosus, a juvenile dermatomyositis, as well as advances in molecular biology, have assisted epidemiologic study of the rheumatic disorders of childhood. It may be misleading to extrapolate the incidence and prevalence of pediatric forms of arthritis from population studies of adults. Additional study of the frequency of childhood musculoskeletal disorders is very much needed. Classification criteria for Kawasaki syndrome, fibrositis in children, and the juvenile spondyloarthropathies are also desirable.