A 62 year-old man was admitted with a right hemiparesis, sensory aphasia and right hemianopia which appeared on awakening. He was initially thought to have a stroke, but EEG showed diffuse slowing and both CT scan and MRI irregular white matter lesion suggesting a leucoencephalopathy. His neurological deficit regressed, and he was discharged after 2 weeks. He was readmitted 6 months later because of mental confusion. MRI revealed diffuse white matter lesions extending up to the frontal lobes, these were hyperintense on T2 weighted images and suggested the diagnosis of gliomatosis cerebri (GC). The patient became progressively comatose and died 6 weeks later. At autopsy the brain looked diffusely swollen with irregular greyish areas of the white matter of both centrum ovale and brain stem. On microscopic examination the cerebrum and brain stem were diffusely and asymmetrically infiltrated by numerous neoplastic glial cells without angiogenesis or disruption of architectonic boundaries. There were no mitoses nor necrosis. Many tumour cells were GFAP- and S100-positive. A high proportion of cells contained the leucocyte antigen Leu-7. This case of gliomatosis cerebri is compared to the 9 published cases of GC with an initial focal neurological deficit and to the 19 publications reporting MRI results. The controversial nosological boundaries and etiopathogenetic hypotheses of this peculiar neoplastic disease are discussed.