Abstract To assess the changes in arterial structure resulting from subarachnoid hemorrhage, morphometric analysis was performed on basilar arteries from rabbits that had received an experimental subarachnoid hemorrhage up to 6 days earlier. For morphometric determination, the crosssectional area of the media, the area of the lumen, and the length of the internal elastic lamina were measured planimetrically. The morphometric diameter of the lumen, the media-to-radius ratio, and several other morphometric parameters were also calculated. Subarachnoid hemorrhage induced significant biphasic constriction of the basilar artery without any changes in the cross-sectional area of the media. The relative amount of smooth muscle cell decreased significantly in the late stage of hemorrhage.