Moyamoya disease is an occlusive intracranial arteriopathy with an abnormal cerebral vascular collateral network at the base of brain. Despite strict diagnostic guidelines for moyamoya disease, the etiology and pathogenesis remains unknown. There are several reports that moyamoya disease should be regarded as a systemic vascular disorder. However, Moyamoya and coronary artery disease may have common etiologic factors. We decribe here a 35-year-old female with moyamoya disease that was diagnosed as severe coronary artery disease. Coronary angiography showed a left main ostial total obstruction with TIMI grade III collateral blood supply from the normal right coronary artery. We report the first clinical case of moyamoya disease with left main ostial total obstruction in a Korean patient and recommend that an evaluation of the extracranial (especially coronary artery) vascular system should be considered if there is some evidence of coronary artery disease.