Delayed necrosis of the brain following exposure to high doses of radiation is a recognized hazard. It is important to predict the nature of these postradiation changes, since surgical removal of radiation necrosis may reverse neurological deterioration of patients so affected. The importance is stressed of correlating the findings on computed tomography (CT) scans and zones of high radiation dose on dose reconstruction plans to differentiate between delayed radiation necrosis and tumors of the brain. This differentiation is not possible using the criteria of CT alone.