Between October, 1978 and August, 1986, 35 patients with thyroid ophthalmopathy were treated with radiotherapy. Twenty-eight patients had treatment with corticosteroids prior to radiotherapy and either progressed on steroids or relapsed during tapering. Seven patients with contraindications to steroids were treated primarily with radiotherapy. After radiotherapy, 25 patients (71%) did not require any further steroids or orbital decompression and ten (29%) failed. Patients who required steroids or decompression for active disease after radiotherapy were considered treatment failures. A total of 14 (40%) patients required eye muscle or lid surgery for correction of stable soft tissue defects after radiotherapy, more commonly in patients treated with radiotherapy after steroids or decompression than those irradiated primarily; the median time between radiotherapy and surgery was 8 months (range 1-48). Various factors were examined for prognostic significance in predicting radiotherapy failure. Review of the interval between onset of eye disease and radiotherapy demonstrated that six of ten (60%) failures versus only five of 25 (20%) successful treatments received radiotherapy within 6 months of onset of eye disease. No relation between outcome and sex, age or hyperthyroid versus euthyroid Graves' disease was apparent. Radiotherapy has been used for patients with thyroid ophthalmopathy who failed steroids, decompression, or had steroid contraindications. Morbidity of radiotherapy was minimal and most patients were spared the morbidity of continued steroid therapy.