I-131 treatment of Basedow's disease is effective and safe. Relatively high energy doses to the thyroid in the range of 150-200 Gray are needed in endemic goiter areas, where immunogenic hyperthyroidism may coincide with functional autonomy. Induction of euthyroidism by low doses of antithyroid drugs (methimazole, carbimazole) before I-131 treatment prevents complications and has no significant influence on outcome of I-131 therapy. As compared to alternative therapeutic modalities, the risks of I-131 are low.