Ninety-two patients with Kawasaki disease were treated with five different types of drug therapy: a steroid preparation (prednisolone), aspirin, an antibiotic, a combination of steroid plus aspirin, and a combination of steroid plus warfarin. One or two months after the onset of the disease, coronary angiography demonstrated coronary aneurysms in 20% of cases treated with an antibiotic alone, 64.7% of cases in the steroid-treated group, and 11% of those in the aspirin-treated group. These findings suggest that the steroid might act adversely to cause a progression of coronary lesions of the disease. The aspirin-treated group did not have a significantly lower incidence of coronary lesions compared with the group treated with an antibiotic alone. But in view of the fact that the direct cause of sudden death of the disease is thrombotic occlusion of a coronary artery, aspirin might act as the effective means for prevention of sudden death due to Kawasaki disease.