Gliomatosis cerebri is rarely encountered and its intra vitam diagnosis has remained difficult. We present biopsy and autopsy findings in three cases that are representative of diffuse glioma, gliomatosis cerebri and diffuse glioblastosis, a modification of the subclassification proposed by Zülch31. Stereotactic biopsy in conjunction with nuclear magnetic resonance tomography (MRT) is recommended as the diagnostic procedure in suspected cases. Immunohistochemical examination with a panel of neuroectodermal markers is helpful in the differential diagnosis but has to take into account that reactive astrocytes may be closely intermingled with the neoplastic glial cells.