Superficial siderosis (SS) of the central nervous system is a rare condition in which hemosiderin is deposited in the subpial layer of the brain and/or spinal cord. It is supposed that hemosiderin deposition is a result of recurrent or persistent hemorrhage in the subarachnoid space. The causes of hemorrhage are tumor, vascular abnormality, injury, dural defect, and others. The source of hemorrhage is not apparent despite of extensive examinations in about a half of the patients with SS. Patients with SS usually reveal slowly progressive and irreversible cerebellar ataxia and/or sensorineural hearing loss. MRI of T2WI or T2*WI demonstrates characteristic linear low intensity along surface of the brain and the spinal cord. There are two types of SS. One is a classical type, in which low intensity of MRI is diffuse and symmetrical. The other is a localized type. We attempted to make a clinical criteria of SS according to the world literature. Then, the criteria was applied to cases (53 cases of classical type and 7 cases of localized type) which are collected from Japanese nationwide questionnaires. The causes and symptoms of Japanese SS are similar with those of Western countries.