To evaluate the influence of radiation volume and other risk factors for the development of delayed radiation toxicity in patients treated for low-grade glioma, a retrospective analysis of 41 adult patients treated with focal or whole brain radiotherapy (WBRT) was performed. For all patients CT and MRI scans were revised to quantify brain atrophy and white matter lesions. Medical data were reviewed concerning baseline and tumor characteristics, treatment, survival, signs and symptoms of clinical encephalopathy and cardiovascular risk factors. In patients treated with WBRT an increased risk was found for brain atrophy (RR 3.1), white matter lesions (RR 3.8) and clinical encephalopathy (RR 4.2). An increased risk of atrophy (RR 2.2) and white matter lesions (RR 2.9) was also found in patients aged over 40 years. Furthermore, brain atrophy and white matter lesions were more severe in patients treated with WBRT and in older patients. In conclusion, both the incidence and the severity of abnormalities is greater in patients treated with WBRT and in older patients.