Kawasaki disease or mucocutaneous lymph node syndrome is an acute inflammatory illness of childhood characterized by systemic panvasculitis. It presents with high fever, dramatic changes of the skin and mucous membranes, and lymphadenopathy. Adult-onset Kawasaki disease is rare and reports on coronary involvement in adult are even rarer. Herein, we report a case of adult-onset Kawasaki disease complicated by splenic infarction and development of coronary aneurysm even despite of treatment with intravenous gamma globulin. A 20-year-old man presented with fever, erytheatous rash, induration and desquamation of hands and feet, pulmonary edema and shock due to cardiomyopathy, splenic infarction, bilateral conjunctivitis, jaundice, and cervical lymphadenopathy. After Kawasaki disease was suspected, intravenous gamma globulin (2 g/kg once) and aspirin (6 g/day) were administered. On the 30th hospital day, transesophageal echocardiography showed one coronary aneurysm and coronary angiography showed three aneurysms. Eight months after the first admission, follow-up coronary angiography showed normalization of the previous coronary abnormalities.