Abstract: Effectiveness of radioiodine for Graves' hyperthyroidism depends on retention time of ¹³¹I in the thyroid, and may be effected by several factors, including previous treatment with antithyroid drugs, goiter volume, 24 h thyroidal radioactive iodine uptake and so on. A short course of therapy with low dose of lithium carbonate increased retention of ¹³¹I in the thyroid and prolong the intrathyroidal effective half-life of ¹³¹I before and after ¹³¹I therapy in patients with Graves'disease, because of the actions that lithium blocks the release of organic iodine and thyroid hormone from the thyroid gland without affecting thyroidal radioactive iodine uptake. Therefore, using lithium as adjunct to radioiodine therapy increases the radiation dose delivered to the thyroid, to result in reduced the activity required and whole-body radiation dose in patients with very short effective half-life, and so improve the cure rate of hyperthyroidism. A short course of lithium carbonate therapy can be considered a useful adjunct to ¹³¹I therapy for obtaining a more rapid control of thyrotoxicosis and avoiding its transient exacerbation because of methimazole withdrawal prior to ¹³¹I administration or in patients who cannot tolerate or do not respond to antithyroid drugs, and for helping to prevent the radioiodine-associated increase in serum free thyroid hormone concentrations. In addition, lithium carbonate enhances the effectiveness of ¹³¹I therapy, in terms of prompter control of hyperthyroidism in patients with small or large goiters. At the same time, lithium also may increases the rate of permanent control of hyperthyroidism in patients with large goiters. In summary, in the short-term lithium plays an important role as an adjunct to ¹³¹I, since it helps to prevent the ¹³¹I-associated increase in serum free thyroid hormone concentrations and allows a more prompt control of thyrotoxicosis. This is of particular importance in highrisk patients, such as the elderly, those with severe hyperthyroidism, underlying cardiovascular disorders, or other severe nonthyroidal illness for whom even a transient exacerbation of the thyrotoxicosis may be dangerous. Treatment with a relatively low dose of lithium before and after ¹³¹I therapy offers a safe and effective alternative means of controlling thyrotoxicosis in patients with Graves disease.