The authors report successful surgical treatment of a patient with an anterior communicating artery aneurysm associated with absence of all of the left cervical carotid arteries. A review of the previous reports of 15 cases of intracranial aneurysm in association with absence of the internal carotid artery emphasizes the rarity of this lesion. Aneurysms with such an association have a distinct distribution different from that observed in the usual population. The data suggest that intracranial aneurysm develops more frequently in the absence of the internal carotid artery as a result of altered hemodynamics.