The effects of orbital irradiation on Ophthalmic Graves' Disease (OGD) were evaluated in 24 patients. All patients were irradiated after a median duration of eye symptoms of 12 months (range 3-36 months). Irradiation therapy was performed for loss of visual acuity, progressive diplopia and/or keratitis due to recent progression of eye symptoms. During a follow up period of 2-4.5 years, in 11 patients after irradiation, a mean decrease in proptosis oculi of 5.1 mm was found while 8 of these patients showed a mean increase in visual acuity of 0.26. Apparently, a decrease of activity of the inflammatory process in retrobulbar tissues can be achieved after irradiation, over a longer period of time in many patients. Furthermore concomitantly administered corticosteroids could be tapered off completely in all patients. Treatment of severe OGD of recent onset with irradiation, in combination with a short course of prednisone is very effective. This study also shows that prednisone treatment alone is not very successful because of the high recurrence rate of eye sings after decrease of the dose and the many side effects of the drug.