Four cases of gliomatosis cerebri are reported that demonstrate the variability of the clinical course. A review of these and 32 cases from the literature revealed that the most striking finding was change in personality and mental status. Hemiparesis, ataxia, papilledema, headache, seizure, and brainstem signs were the next most common clinical findings. Laboratory and radiographic tests, including angiography and pneumoencephalography, often showed only minor and nonspecific changes in the face of profound mental deterioration. Increased intracranial pressure usually occurred late but was probably an important factor of the terminal course in most patients. The pathologic changes were typical, with diffuse infiltration of astrocytoma cells through brain stem, subcortical white matter, and, to a lesser extent, cerebral cortex.