OBJECTIVE To observe indication and effectiveness of radiation therapy (RT) in the treatment of the patients with thyroid-associated ophthalmopathy (TAO). METHODS 23 patients of TAO who received RT in Sichuan University were collected from 1992 to 2004. Among those patients, 9 cases of infiltrative exophthalmos and 14 cases of compressive optic neuropathy were ineffectively with glucocorticoid treatment or could not treated with glucocorticoid, or could not perform orbital decompression due to severe diabetic mellitus or hypertension, or feared to receive the operation, all of patients were active ophthalmopathy and with short duration. Outer orbital radiation was applied using linear accelerator with Donaldson's method, radiation treatment fields was 4 cm x 5 cm, exposure energy was 2 GY fractions with total of 20 GY. In 11 cases with severe inflammation prednisone was administered during radiotherapy. Photos and CT scan were taken for each patient before and after RT. RESULTS Visual acuity (VA) of the patients was improved from before RT 0.04 - 0.2 to after RT 0.1 - 0.8 in 14 cases of compressive optic neuropathy. Extraocular muscle of patients decreased in size confirmed by CT scan. VA improvement was correlated with the degree of extraocular muscle decreased in size. Eyelid and conjunctive swelling, eyelid incompletely closure, exposure keratitis, limitation of motion and proptosis were improved after RT in 9 patients with infiltrative exophthalmos. Following up the patients for 1 - 3 years, it was found that VA decreased in 3 cases and inflammation recurred in 4 cases, eyelids could not closed in 2 cases after RT. CONCLUSIONS RT could be used in severe, active cases of TAO. If there is severe inflammation, steroids could be combined with RT therapy.