Moyamoya disease is a vasculopathy of the internal carotid arteries, leading to progressive intracranial arterial occlusion and moyamoya syndrome is reserved for individuals with a known risk factor for the condition. Moyamoya syndrome has an increased incidence in other genetic syndrome but the etiology remains unknown. It has been suggested the involvement of genetic factor in its pathogenesis of moyamoya disease and some reports has been presented about the role of genetics in moyamoya disease by mapping of chromosome. On the other hand, Williams syndrome is well known of microdeletion disorder at chromosome 7q 11.23 with a hallmark feature of generalized arteriopathy presenting as stenosis of elastic arteries and hypertension In 1993, the case of Williams syndrome complicated by moyamoya disease was reported one and only in but an autopsied case. We report a case of symptomatic moyamoya syndrome with Williams syndrome undergoing successful surgical intervention and suggest the mechanism of coincidence on the basis of genetic defect. Key Words: Moyamoya disease, Williams syndrome, Elastin, arteriopathy