The authors report the clinical course, radiographic findings, and gross and microscopic pathology of a patient with fatal rupture of the supraclinoid segment of the left internal carotid artery during transluminal angioplasty for subarachnoid hemorrhage-induced vasospasm. The rupture most likely resulted from a small portion of aneurysm neck which remained unclipped, thereby leaving an area of structural weakness in the arterial wall at the site of clipping. The area of structural weakness predisposed the artery to rupture upon the addition of transmural pressure induced by balloon inflation during transluminal angioplasty. Caution is advised when performing transluminal angioplasty in the region of aneurysm clipping since the vessel lumen "recreated" during the clipping procedure may contain some residual and structurally incomplete aneurysm neck in the vessel wall.