Gliomatosis cerebri is a rare tumor of neuroepithelial origin presenting as deterioration of cognitive function, seizure, and psychomotor retardation. Since 1988, we have seen nine cases of gliomatosis confirmed by biopsy. Headache, seizure, visual disturbance, dementia, motor weakness were the initial predominating clinical features in these cases. MRI was much better in delineating the extent of tumors by showing ill-defined high signal intensity on T2-weighted images. Histological examination of brain biopsy disclosed a diffuse proliferation of neoplastic glial cells infiltrating into well-preserved underlying cytoarchitecture. The diagnosis of glimatosis cerebri was formerly made only at autopsy. However, recent improvements in neuroimaging techniques and biopsy now allow for antemortem diagnosis.