Occurrence of dissecting aneurysm of the common carotid artery after arteriography in 2 patients is reported. In 1 patient, the artery was narrowed sufficiently to produce massive cerebral infarction. In the other, the hemorrhage was small and was an incidental autopsy finding. Large autopsy surveys indicate that a significant percentage of patients subjected to arteriography develop a small dissecting aneurysm. Lesions large enough to occlude the lumen are extraordinarily rare, but a few have been reported. Nevertheless, even the smallest intimal elevation may become the site of thrombus formation and, thus, a possible source of emboli.