Inadequate understanding of the pathogenesis and etiology of vascular inflammation continues to hinder progress in the diagnosis and treatment of pediatric vasculitis. The greatest amount of work is being done in the most common vasculitides of childhood, including Kawasaki disease and Henoch-Schönlein purpura. Discussion of rarer types of vasculitis, on the other hand, such as antineutrophil cytoplasmic antibody–positive small vessel diseases, is largely restricted to case reports. Most aspects of the care of children with Wegener granulomatosis and microscopic polyangiitis are derived by extrapolating from data about adults. Virtually no data are available concerning ways in which these diseases may be different in children.