We report a 35-year-old man with gliomatosis cerebri, of which fluid-attenuated inversion-recovery (FLAIR) and T2-weighted magnetic resonance (MR) images revealed diffuse and high signal intensity areas in the bilateral cerebral hemispheres, bilateral middle cerebellar peduncles, cerebellum and lumbosacral spinal cord. Malignant features were not detected by 123 I-IMP SPECT, 201TI SPECT, 18F-fluorodeoxyglucose PET or MR spectroscopy. Histopathological examination of biopsy specimens from the right frontal lobe demonstrated diffuse infiltration of neoplastic cells with relative preservation of the underlying cytoarchitecture. Gliomatosis cerebri demonstrating a lumbosacral spinal cord lesion on MR images is rare and thus this case is important from the aspect of the differential diagnosis of spinal cord lesions.