Optic neuropathy resulting in permanent visual loss is an infrequent delayed complication of radiation therapy. Hyperbaric oxygen therapy (HBO) has been used to treat such a complication, but its efficacy is controversial. We report a patient who presented with radiation-induced optic neuropathy 17 months after irradiation for a left maxillary antrum melanoma. HBO fully reversed visual loss in the more recently involved eye, and slightly improved vision in the earlier affected eye.