MR examinations of 104 patients who had undergone radiotherapy to the brain were reviewed. Thirty-six patients received Gd-DTPA enhanced study during the course of MR evaluation and six of the patients showed enhancing radiation necrosis. Histopathological confirmations were obtained in three patients. Gd-DTPA enhancing radiation lesions were multiple and patchy in three patients, multiple and patchy with cyst formation in two and ring shaped in one. In terms of their distribution, enhancing lesions in four patients were seen only in the white matter within the irradiated field and these patients had undergone radiotherapy within five years. The interval after radiotherapy was more than eight years in two patients and their enhanced lesions were observed in both the white and gray matter. Histopathological findings of Gd-DTPA enhancing radiation necrosis were gliosis and coalescing vacuoles of the neural tissue. None of these enhanced radiation lesions showed significant mass effects. Patterns of the enhancement were not specific. It was considered to be difficult to differentiate tumor recurrence from radiation necrosis with conventional Gd-DTPA enhanced MR examinations. In one patient, delayed MR images after Gd-DTPA administration showed increases in the size and number of radiation enhanced lesions. Dynamic and delayed MR study might add more information to conventional imaging after Gd-DTPA. Further studies are necessary to differentiate radiation lesions from tumor recurrences.