6 autopsy cases of primary leptomeningeal sarcomatosis are presented as a distinct nosological entity with a variable clinical picture and morphology in 5 males and 1 female. The clinical course from onset of symptoms till death ran for only a few weeks in most cases. 2 infants showed brain tumor symptoms and signs. 2 patients of advanced age presented a polyradiculoneuritic syndrome and 2 young adults had spinal cord compression symptoms and a mixed clinical form. In almost all cases, clinical symptoms and signs were for most of the course confined to one part of the neuraxis. The CSF was distinctly abnormal in all cases, showing elevated protein, depressed glucose and pleocytosis of variable extent. CSF sediment was investigated in 3 cases in all of which malignant tumor cells were found so a diagnosis of malignant meningeal tumor was made during life. Electron microscopy of CSF cells in 1 case confirmed the primitive character of the tumor cells. Complete autopsies revealed absence of any neoplasm outside of the CNS. Gross meningeal involvement was visible in all cases. Histologically, 3 tumor types were distinguished: polymorphic cell sarcoma, an undifferentiated form, and fibrosarcomatosis. Clinical data are analyzed in order to distinguish the condition from other neoplasms or infectious, especially tuberculous meningeal infiltrations. CSF cytology studies are considered the most useful step in clinical diagnosis. Neuropathological features are reviewed with stress on differentiation from malignant lymphomas of the CNS, diffusely spreading medulloblastoma, meningeal melanoblastosis and gliomatosis. The origin of meningeal sarcomatosis cells is briefly discussed. The use of the term "meningeal meningiomatosis" for this condition is deprecated.