Moyamoya disease is characterized by bilateral progressive obliteration of the terminal internal carotid arteries. It is relatively common in Asian populations and is found more frequently in children, who present with symptoms and signs of cerebral ischemia, often provoked by hyperventilation during crying or eating hot food. In adult age, more patients present with intracranial hemorrhage. To differentiate moyamoya disease from other cerebrovascular diseases, the diagnosis has been defined according to a guideline provided by the 'Research Committee on Spontaneous Occlusion of the Circle of Willis'. Bilateral stenosis and/or occlusion with moyamoya vessels documented by cerebral angiography or MRA/MRI are the key points in diagnosis. Since its etiology is still unknown, prevention of progressive cerebral ischemic insult is the current target of treatment. Revascularization surgery, such as indirect or direct extracranial-intracranial bypass surgery can fulfill this goal. Early detection and treatment, especially in childhood, is most important for the better prognosis of this disease.