This could be the first case of bilateral agenesis of the internal carotid artery reported "in vivo." Angiogrpahic study has allowed us to recognize the anatomic details of this malformation. The absence of the two carotids is being compensated for by a trigeminal artery on the (left) side and by a hypertrophied accessory meningeal artery on the (right) side. Standard x-rays of the base of the skull (including tomography) revealed a dilation of the foramen ovale, related to the hypertrophied right accessory meningeal artery, and a complete atresia of the two carotid canals. This latter finding permits us definitely to postulate the nature of the congenital anomaly. Finally, the carotid agenesis was associated with the presence of three arterial aneurysms, situated respectively in each carotid territory and in the territory of the basilar artery.