We analyzed clinical data from 195 patients (141 boys) with myocardial infarction complicating Kawasaki disease, collected from 74 major hospitals in Japan. The myocardial infarction usually occurred within the first year of illness, but 27.2% of the patients had myocardial infarction more than 1 year later. In 63% of the patients it occurred during sleep or at rest. The main symptoms of acute myocardial infarction were shock, unrest, vomiting, abdominal pain, and chest pain; chest pain was much more frequently recognized in the survivors and in older patients. The myocardial infarctions were asymptomatic in 37% of the patients. Twenty-two percent of the patients died during the first attack. Sixteen percent of the survivors of a first attack had a second attack. Forty-three percent of all survivors of the first or subsequent attack are doing well; however, others have some type of cardiac dysfunction, such as mitral regurgitation, decreased ejection fraction of the left ventricle, or left ventricular aneurysm. Coronary angiographic studies indicate that in most of the fatal cases there was obstruction either in the main left coronary artery or in both the main right coronary artery and the anterior descending artery. In survivors, one-vessel obstruction was frequently recognized, particularly in the right coronary artery.