Moyamoya disease is an obstruction of the internal carotids and of the afferent and efferent channels of Willis polygon, which causes a collateral circulation, responsible for the typical angiographic image of a "puff of smoke" (Moyamoya, in Japanese). Its etiology is unknown, and it might be congenital or acquired. The clinical features are cerebral ischemia, recurrent transient ischaemic attacks, sensorimotor paralysis, convulsions and migraine-like headaches. We report a 2 years and 9 months old boy with Down syndrome and Moyamoya disease who presented with focal convulsions.