Leptomeningeal gliomatosis is reported in three patients in whom the tumor involved the central nervous system diffusely. Clinically, these patients presented with varying combinations of both non-localizing and focal symptoms and neurologic signs. Most notable were meningismus, vomiting, headache, altered level of consciousness and papilledema. Laboratory findings included high CSF protein, high CSF pressure and hydrocephalus but no direct evidence of neoplasia. All three patients received surgical treatment for hydrocephalus. Brains were swollen on gross examination with leptomeningeal thickening resulting from diffuse infiltration of tumor cells in the leptomeninges. In two of the patients small parenchymal gliomas in the brain were probably the source of the meningeal tumor.