Although postoperative radiotherapy (RT) is widely used in patients with low-grade gliomas (LGGs), its clinical benefit remains unproven. Because LGGs include diseases with many different histologies, cytogenetic patterns, and natural histories, evaluating the effect of any treatment for LGGs is difficult. Analysis of prognostic subgroups has shown median survival rates ranging from 1 to 10 years. The clinical benefit of postoperative RT in LGGs in retrospective studies is confounded by the heterogeneity of LGGs and treatment-related variables. These studies report conflicting results, most likely because of differences in patient populations. The only prospective, randomized trial comparing postoperative RT with observation failed to show a survival benefit but showed a modest, although statistically significant, improvement in time to progression. Given that two thirds of patients in the observation group received RT at progression, the absence of a survival benefit suggests that RT is active in LGGs, but that delayed RT may provide the same survival advantage as postoperative RT. Moreover, high-dose or whole-brain RT can cause cognitive deficits. Our opinion is that postoperative RT should not be administered routinely to patients with LGGs. If RT is deemed necessary, such as in progressive or inoperable disease causing neurologic symptoms, a total dose of </=50 Gy with a fractional dose of </=1.8 to 2 Gy should be administered using modern, highly conformal techniques. Ideally, RT should be used only within the context of clinical research protocols.