Neuroradiologic diagnosis of "gliomatosis cerebri" is hampered by the diffuse, isodense character of the lesion, and the fact that it may not enhance when intravenous contrast medium is administered. Clinical signs and symptoms are usually nonspecific, nonfocal, and disproportionately mild. We report a case of diffuse glioma in a 30-year-old man, discuss the difficulty in arriving at a precise diagnosis of gliomatosis cerebri, and examine the possible role of MR in its detection and delineation.