Segmental mediolytic arteriopathy (SMA) is an uncommon nonatherosclerotic and nonvasculitic arteriopathy. This disease is characterized by lytic degeneration of the arterial media, intramural dissection and thrombosed or ruptured aneurysm. SMA mainly involves the intraabdominal arterial system, resulting in intraabdominal and retroperitoneal hemorrhage. However, only a few cases of SMA with involvement of intracranial arteries have been reported. Here, we present a case of SMA developing subarachnoid hemorrhage due to dissection of the internal carotid and vertebral arteries. This patient was a 48-year-old male who died 13 days after admission for sudden loss of consciousness. Computed tomography showed subarachnoid hemorrhage. At autopsy, the affected vessels included the right vertebral, left internal carotid, superior mesenteric, bilateral renal and left external iliac arteries. Histopathologically, the arteries showed segmental lytic degeneration and disappearance of medial smooth muscle cells, medial dissection and formation of pseudo-aneurysms, the wall of which consisted of a thin membrane of the adventitia. These histopathological features mimicked an entire wall dissection type of intracranial dissecting aneurysm, which exclusively affects the vertebro-basilar system. Thus, SMA should be considered a possible underlying disease in patients with spontaneous dissection of intracranial arteries.