Despite the availability of effective treatments for Graves' disease, there are patients who are unable to tolerate, or choose not to accept, current therapies (oral medication, radioactive iodine, or surgery). In this study, we have examined the use of thyroid arterial embolization as an option for patients who suffer from Graves' disease and who fit into one of the preceding patient groups. Selective arteriography, followed by embolization of thyroid arteries, was performed using Seldinger's technique in 22 patients with Graves' disease. Six of the patients received both arterial embolization and surgery at 2-3 wk after embolization. No serious complications were noted in any patient. In those who were treated with only interventional embolization, 14 of 22 (63.6%) became euthyroid and remained in this state for the duration of the study. The remaining 2 patients required a maintenance dose of antithyroid drug therapy (tapazole, 5-10 mg/d; or propylthiouracil, 50-100 mg/d). Patients were followed for a median time of 27 months (range, 6-50). At the end of the follow-up period, all 22 patients were euthyroid, the size of thyroid gland had decreased by one third to one half its original volume, but 2 patients continued to require antithyroid drugs. Histologic analysis of thyroid tissue from 6 patients who had embolization followed by surgery showed that embolization blocked both the superior and inferior thyroid arteries plus most of their branches. Evidence of chemical inflammation, necrosis, and fibrosis were observed in embolized thyroid tissue. The average diameter of capillary network within the body of the thyroid adjacent to superior and inferior artery was 0.12-0.25 mm, with the smallest ones ranging from 0.04-0.11 mm. The diameter of the capillaries in the isthmus ranged from 0.13-0.15 mm. The average diameters of the superior and inferior arteries were 2-5.5 and 3-3.75 mm, respectively, measured using radiographs from angiography. Based on the measured diameters of arteries, the appropriate size of embolizing granules can be selected, and complete embolization of the majority of the thyroid glands was achieved with a high frequency of therapeutic success. Histological examination of the thyroid tissue and clinical follow-up after embolization indicate that this procedure is an effective, minimally invasive, and safe method for the treatment of Graves' disease patients who cannot, or choose not to, accept current therapies.