OBJECTIVE : To evaluate the effectiveness of radiation therapy and steroids for Asian patients with Graves' ophthalmopathy using the clinical activity score (CAS), and changes in external ocular muscles and eye proptosis determined by magnetic resonance imaging (MRI). METHODS : We retrospectively reviewed 48 patients who received combined orbital radiation and systemic glucocorticoids in our hospital. MRI was performed both before and 1 month after treatment in all patients. We calculated the areas of five extraocular muscles and the degree of proptosis on transverse sections, and we evaluated the activity of the disease using CAS before and 1 month after treatment and toxicity. RESULTS : The areas of external ocular muscles, the length of eye prominence and CAS were significantly improved by the combination of orbital radiation and steroids. The change in the area of the medial rectus muscle had a significant correlation with the change in CAS (P < 0.05). Graves' ophthalmopathy progressed again in 4 of the 48 patients; however, there were no patients with serious side effects in a median observation period of 41.5 months. CONCLUSIONS : Treatment with the combination of orbital radiation and systemic glucocorticoids is subjectively and objectively effective for Asian Graves' ophthalmopathy without severe toxicity.