 Graves disease GD is the most frequent cause of hyperthyroidism, affecting mainly women aged 40-60 years. Radioiodine 131I, introduced in 1941, has become a cornerstone in the treatment of GD hyperthyroidism. Because of its safety, low costs and rapid effect, it is considered a first line therapy in the United States. However, treatment failure occurs in about 15-25 of patients treated with radioiodine. Patients not cured with the first dose of radioiodine usually present severe hyperthyroidism, characterized by large goiter, high 24-hour radioiodine uptake 24h-RAIU and very high levels of thyroid hormones. We have previously shown that large goiter 48ml is an independent predictor of treatment failure. In these patients, the therapeutic failure was 40.0 while in patients with smaller goiter was only 6.5 P0.005; unpublished. It is generally accepted that higher doses of radioiodine improves cure rates. Indeed, a recent meta-analysis found a correlation between radioiodine dose and therapeutic success in GD patients. To our knowledge, there are no published studies evaluating cure rates with different radioiodine doses in severe GD. 