The authors present angiographic and computed tomographic demonstration of bilateral agenesis of internal carotid arteries. The patient was a seventy-six years old man who had been admitted to our hospital because of right hemisparesis and disorientation. In addition to the left chronic subdural hematoma, computed angiotomography showed the dilated basilar artery and dilated posterior communicating arteries. However, the bilateral internal carotid arteries were not recognized. Burr hole and irrigation were performed, then neurological deficits and symptoms were disappeared. Hematoma was 150 ml. Though axial transverse computed tomograms of base of skull demonstrated the absence of bilateral carotid canals. On aortography, the right common carotid artery and vertebral artery were supplied from the innominate artery and the left common carotid artery and vertebral artery were supplied from the left dilated subclavian artery. Bilateral retrograde brachial angiograms demonstrated the internal carotid circulation, which was supplied through bilateral dilated posterior communicating arteries. Basilar artery was also in a large caliber. Bilateral ophthalmic arteries were opacified from external carotid artery via the middle meningeal artery. Ten cases of bilateral agenesis of internal carotid arteries have been reported previously. The findings of angiograms and computed tomograms on the agenesis of bilateral internal carotid arteries were discussed. This anomaly is important on cerebral hemodynamics and embryology.