Until 1972, Kawasaki disease, or acute febrile infantile mucocutaneous lymph node syndrome (MCLS), was considered in Japan to be a nonfatal disease with a favorable prognosis. Based on the findings from two autopsy cases of MCLS, we believe that sudden and unexpected death during convalescence may be due to arterial lesions, especially those involving the coronary artery, that resemble those of periarteritis nodosa. Of 29 autopsy cases of MCLS, gathered from all over Japan, all exhibited arteritis lesions (eg, aneurysm due to coronary arteritis). Such vascular pathological findings may in fact represent the same entity as infantile periarteritis nodosa. Whether infantile periarteritis nodosa can be identified with the adult type is still debatable. The particular manifestations of infantile periarteritis nodosa might be related to severe vasculitis. Autopsy cases of infantile periarteritis nodosa without MCLS manifestations are being collected and studied.