Histopathology, distribution and incidence of vascular changes were studied in tissues obtained at autopsy on thirty-seven children. Elastic and musculoelastic arteries showed a high incidence of arteritic changes, however the degree of the lesions was in general mild to moderate with the exception of the iliac artery, which revealed severe changes and a necrotizing panarteritis which was often accompanied with an aneurysm formation. A high incidence of arteritic changes, of which main histological feature was necrotizing panarteritis, was seen in extravisceral middle sized arteries. The coronary artery in particular was involved in each case and most had an accompanying aneurysm, some of which had ruptured. Intravisceral small sized arteries showed a relatively low incidence of arteritic changes and the degree of inflammation was in general mild. Phlebitis was present in over half the number of patients. The degree of lesions was mild in the small veins and mild to moderate in the large veins. Vascular lesions in Kawasaki disease should be termed systemic vasculitis rather than a systemic arteritis. There was a correlation between the caliber of involved vessels and the degree of vascular lesions. According to the histopathology, distribution and incidence of angitis, Kawasaki disease does resemble infantile periarteritis nodosa with the exception of the different manner of the coronary and iliac involvement.