Gliomatosis cerebri is a rare form of glioma, which diffusely extends to both cerebral hemispheres. Because it sometimes fails to show severe neurological symptoms in spite of diffuse invasion, the antemortem diagnosis is difficult. We report a case of a 77-year-old woman, who was admitted with progressive left hemiparesis and dysarthralgia. Plain CT scan of the brain showed almost no abnormal findings. MRI T2-weighted image revealed widespread and nearly symmetrical extension of a high intensity area from the corpus callosum to the deep white matter of both cerebral hemispheres. Open biopsy of the brain showed glioblastoma multiforme, which finally confirmed the clinical diagnosis of gliomatosis cerebri. We also review the classic and recent literatures.