Coronary artery aneurysms are not uncommon. They are usually arteriosclerotic in origin, and may be congenital or secondary to injury, dissection, infection, inflammation, or Kawasaki disease (KD). Herein, we report a case involving a 25-year-old male smoker with acute myocardial infarction (AMI). Coronary angiography showed triple-vessel disease, coronary artery aneurysms, and diffuse ectasia. Coronary artery bypass grafting was performed without complications. Based on his history, serologic examinations, and angiographic findings, we suspected that his coronary artery aneurysms and ectasia were the adult sequelae of KD. This case is a good reminder that KD victims may suffer from young-onset AMI.