An autopsy case of abnormal Intracranial vascular networks at the base of the brain corresponding to so‐called rete mirabile, associated with occlusion of bilateral internal carotid arteries was reported. This patient was a 62 year‐old female who died about two months after sudden onset of subarachnoid hemorrhage. At autopsy, abnormal vascular networks termed as rete mirabile were observed to be collateral blood supplies among the cerebral regions with flow of the anterior, middle, and posterior cerebral arteries, caused by long‐stading obstruction of bilateral internal carotid arteries at the syphon level. Morphometrical analysis was done by measuring the length of internal elastic membrane of the internal carotid arteries in cross section, and comparing it with those of controlled persons of the same sex and age without any intracranial disorders and hypertensive histories. The result that no significant difference was observed between the former and the latter values suggested that the unusual cerebro‐vascular disorder of this case developed not on the base of congenital anomaly including hypoplasia of internal carotid arteries or arteriovenous malformation but as an acquired lesion established for a lo