The CT features of 45 cases of delayed radiation encephalopathy (including radiation necrosis) following radiotherapy for nasopharyngeal carcinoma are reported. The brain lesions were uni- or bilateral and involved mainly the white matter and subsequently the gray matter of the lower portion of the brain included within the portals of irradiation and its vicinity. The lesions were edematous and hypodense on CT and showed postcontrast enhancement in 50% of the cases. Within the period of follow-up (1-5 years), the lesions showed remissions and exacerbations and in some cases stabilized. In addition, there was progressive cerebral atrophy, manifesting itself mainly as dilatation of the temporal horns, the neighboring cisterns, and sylvian fissures. In some cases that were followed for a long time, the cerebral lesions showed either foci of calcification or encephalomalacia and/or porencephaly.