We report a sibling case of Nasu disease. A 35-year-old housewife, whose parents were consanguineous and whose sister died of the same disease, developed dementia, followed by bone fracture, incontinence and convulsions. She died at age 41. Pathologically, characteristic membranocystic changes of the fat cells in bone marrow and adipose tissues were observed. Neuropathologically, there was demyelination associated with intense gliosis and numerous axonal spheroids in the cerebral white matter. At the electron microscope level, these spheroids were an accumulation of various cell organelles. In addition, some had Hirano bodies. Incontinence was correlated with reduction of the number of nerve cells in Onuf's nucleus of the sacral cord.