In this review, the causes of thyrotoxicosis and the treatment of syndromes with increased trapping of iodine are discussed. The benefits and the potential side effects of 3 frequently used therapies--antithyroid medications, thyroidectomy, and (131)I treatment--are presented. The different approaches to application of (131)I treatment are described. Treatment with (131)I has been found to be cost-effective, safe, and reliable.