The authors report the case of a patient with transient ischemic attacks who was evaluated by duplex scanning, which demonstrated total carotid artery occlusion. Arteriography revealed what appeared to be a classic "string sign" in the cervical carotid artery, and a standard endarterectomy was planned. At surgery the internal carotid artery was found to be congenitally atretic, accounting for the string appearance of the arteriogram. The etiology, associated anomalies, differential diagnosis, and diagnostic evaluation of such lesions are discussed.