Bilateral hypoplasia of the internal carotid arteries is a rare condition. The authors experienced two cases of bilateral hypoplasia of the internal carotid arteries. In one case, a 46-year-old female patient, presented with subarachnoid hemorrhage. Internal carotid angiograms showed right hypoplastic internal carotid artery and left agenetic internal carotid artery. An aneurysm, believed to be the source of the subarachnoid hemorrhage, took origin from the trunk of the basilar artery. In another case, a 48-year-old male, presented with semicomatous mentality. Brain CT demonstrated intracranial hemorrhage on the parasylvian area, and high density on the basal cistern, quadrigerminal cistern and temporal horn of left lateral ventricle. Initially, aortic arch injection did not visualized the origin of the common carotid arteries. It revealed only the vertebral arteries and both external carotid artery originating from each vertebral artery. A selective left vetebral artery study demonstrated a communication between the hypertrophied basilar artery and the posterior cerebral arteries. The anterior and middle cerebral vessels, in turn, were opacified through the circle of Willis, via the posterior communicating arteries. In addition, an aneurysm, believed to be the sourse of the subarachnoid hemorrhage, took origin from the posterior cerebral artery. The cases of the bilateral hypoplasia of internal carotid artery with intracranial aneurysm are reported as above, together with literature review.