Normal high-resolution computed tomographic (CT) scans of 126 patients were reviewed to define the diameter, height of the bifurcation, and transverse position of the normal basilar artery. The mean diameter of the normal basilar artery is 3.17 mm at the level of the pons. In 92% of normal subjects, the basilar bifurcation is located in the interpeduncular cistern adjacent to the dorsum sellae or in the suprasellar cistern below the level of the floor of the third ventricle. In 98% of normal individuals, the basilar artery courses in the midline or in a paramedian position, medial to the lateral margins of the clivus and dorsum sellae.