Moyamoya disease describes a cerebral arteriopathy characterized by stenosis or occlusion of the terminal internal carotid and/or the proximal middle cerebral arteries. We report a female child with trisomy 21 and bilateral moyamoya disease who presented, unusually, with a presumed perinatal cerebral infarct. The clinical, radiological, and angiographic features of moyamoya disease in children with Down syndrome are similar to those with other aetiologies or idiopathic cases. Early recognition is important as moyamoya disease presenting in childhood is associated with a high rate of recurrent stroke and there is evidence that surgical revascularization can prevent further events. An important practical lesson arising from this case is that although the evaluation of children with presumed perinatal stroke tends to be limited relative to the evaluation of arterial ischaemic stroke in older children, this may need to be more comprehensive in infants at high risk of arteriopathy. The parents of the child gave informed consent to the publication of this report.