Giant coronary artery aneurysms are a complication of Kawasaki disease and can be fatal if associated with thrombosis. We describe the clinical outcome of a boy with Kawasaki disease who exhibited “supergiant” coronary artery aneurysms at the age of 14 months and, despite treatment with anticoagulant and antiplatelet medication, developed a left coronary artery thrombosis and presented following a myocardial infarction at 2 years old. Although his symptoms were minimal, the myocardial infarction was identified by abnormal Q-waves and giant negative T-waves in precordial leads of routine electrocardiography. Intensive anticoagulant therapy combining heparin injections and high-dose warfarin was successful. The abnormal Q-waves and negative T-waves had completely disappeared 2 weeks later, likely in association with confirmed reperfusion. On the basis of prompt identification of abnormal Q-waves by electrocardiography, the patient could avoid thrombolytic therapy and catheter or surgical intervention.