Arteries that belong to the central nervous system (CNS) have thick and monotonous internal elastic lamina (IEL), Willis ring, and no collateral branch to the systemic circulation. These characteristics suggest that the circulation of the CNS is constant. In order to know how flow controls the arterial configuration of the CNS, flow of the vertebral and basilar arteries was increased experimentally using eight adult male Japanese white rabbits. Flow increase was induced by the simple ligation of the bilateral common carotid arteries (ligation group, n = 4) or by the ligation of the bilateral common carotid arteries at 1 week after arteriovenous fistula (AVF) between the left common carotid artery and the left external jugular vein (ligation plus AVF group, n = 4). Cineangiography revealed distinct flow increase in the ligation group at 5 weeks after ligation and in the ligation plus AVF group at 5 weeks after AVF (4 weeks after ligation). Vertebral and basilar arteries were remarkably dilated and elongated. Histopathologically, severe disruption of the IEL and focal thinning of the media were distinct. Endothelial cells were preserved and there was no inflammatory cell infiltration. These morphological features are consistent with increased flow-induced adaptive remodeling. It is suggested that the constancy of the flow may give the arterial tree of the CNS these morphological characterizations.