Because of the relative rarity of the conditions, epidemiologic investigation of systemic vasculitis is a challenging prospect. Previous work in this area has been primarily in the form of descriptive studies and therapeutic trials, which have increased awareness of these syndromes among clinicians. However, compared with other diseases, little is known about the epidemiology of the systemic vasculitides. Although significant progress has been made during the past year to estimate incidence and prevalence rates of disease, particularly for giant cell arteritis and Kawasaki disease, further studies are needed to determine risk factors for initial expression and relapses of vasculitis, biologic markers of disease progression, comorbidities, long-term outcomes, and cost of care and disability.