Kawasaki disease (KD) is one of the most important causes of coronary artery aneurysms in children and young adults. However, the natural course of the disease and the patient prognosis remain obscure. A 72-year-old asymptomatic man with undiagnosed KD underwent whole-heart magnetic resonance coronary angiography during a health checkup. The imaging disclosed giant aneurysms in the proximal portion of the right coronary artery and the left anterior descending artery. The patient was successfully treated with coronary artery bypass grafting. The present case suggests that there may be a substantial number of patients who have attained middle to old age with undiagnosed KD.