A mother and daughter presented with a rare combination of moyamoya disease and Graves' disease. A 19-year-old woman experienced numbness in her right hand due to cerebral infarction during therapy for Graves' disease. Cerebral angiography demonstrated stenoses of the bilateral internal carotid arteries and net-like abnormal collateral vessels indicative of moyamoya disease. Her 52-year-old mother with a history of Graves' disease presented with left hemiparesis due to intracerebral hemorrhage; she recovered after hematoma evacuation. Postoperative angiography demonstrated stenoses of the bilateral internal carotid arteries and net-like abnormal collateral vessels indicative of moyamoya disease. Another otherwise healthy daughter manifested slight stenosis of the left internal carotid artery. After cerebral revascularization surgery the patients were able to return to their normal daily lives. These familial cases of moyamoya disease and Graves' disease indicate hereditary involvement in both diseases.