Isolated central nervous system (CNS) granulomatosis resembling sarcoidosis occurred in a 30-year-old woman who had amenorrhea, ataxia, and obstructive hydrocephalus, and a 9-year course of progressive neurological deterioration with recurrent bouts of diabetes insipidus. Lamellar and nodular meningeal hyalinosis resembling amyloid was noted on an initial brain biopsy. At autopsy, the brain had a non-necrotizing granulomatous meningitis and ventriculitis, most prominent at the base of the brain, including the third ventricle and the hypothalamus, but there were no systemic granulomas.