Serial magnification angiography of 7 patients with moyamoya disease revealed (a) previously unreported connections within the abnormal vascular network (AVN), (b) medullary collaterals fed by the AVN and supplying the cortical arteries, and (c) vessels connecting the AVN and the insular branches of the middle cerebral artery. The anatomy of these collaterals and the angiographic features of moyamoya disease are discussed.