Radiation-induced optic neuropathy (RON) is a rare and catastrophic complication of currently employed radiation therapy regimens for meningiomas that have been partially resected and sampled for biopsy. Between 1972 and 1989, 49 patients received postoperative irradiation for partially resected or biopsy sampled meningiomas, with the optic nerve within the treatment field. One patient experienced RON. The latency period for this case was 23 months. A review of the literature disclosed few cases of RON after treatment for meningioma; however, 42 cases of RON have been reported after radiation therapy for other lesions. The authors constructed two approaches to predict optic nerve radiation tolerance. The first is modeled on a previous proposal for a neural tissue nominal standard dose term and enabled accurate prediction of safe treatment regimens and risk of RON. This approach compared favorably with previously employed nominal standard dose terms. The second approach, based on the linear-quadratic model, proved unsuccessful due to its failure to achieve statistical significance.