Severe Graves' ophthalmopathy has been treated in 44 cases by orbital irradiation. 36 out of 37 patients showed a good response or a suspend of the progressive disease. In 17 out of 33 primary irradiations a dose of 10 Gy and in 16 cases a dose of 16 Gy was applied. Measured by ophthalmopathy-index significant better results have been achieved by a total dose of 16 Gy. Because of recurrence after primary irradiation of 10 Gy a re-irradiation became necessary in 35% of the cases. Primary irradiation of 16 Gy has required no further treatment during the same time of observation. A single series of 16 Gy irradiation has shown better results than two series of 10 Gy irradiation concerning the proptosis and alleviation of symptoms.