Moyamoya is a chronic cerebrovascular disease characterized by progressive stenosis or occlusion of the terminal parts of both intermal carotid arteries with telangiectatic vascular network of collateral circulation at the base of the brain and leptomeningeal arteries. The etiology and pathophysiology of this disease are still unknown. Although the idiopathic presentattion is the commonest, moyamoya disease has also been reported in several hereditary or acquired clinical conditions including neurofibromatosis, sickle cell anemia, tuberculous meningitis, atherosclerosis, and following radiation therapy to the head. The term moyamoya disease should be reserved for those cases in which the characteristic angiogrphic pattern is idiopathic; moyamoya syndrome is used when the underlying condition is known. We have experienced a case of coexistence of moyamoya syndrome and hereditary spherocytosis in a 6-year-8-month-old girl who presented with right-sided hemiparesis and pallor. A cerebral angiogram revealed occlusion of proximal portion of left middle cerebral artery and abnormal collateral network. The peripheral blood smear and osmotic fragility test disclosed hereditary spherocytosis. To our knowledge, the coexistence of moyamoya syndrome and hereditary spherocytosis has not been documented. We report here the case and the brief review of related literatures. Further studies are needed to clarify the intimate relationship between the two diseases.