Ablation of the thyroid gland with radioactive iodine-I131 is an effective and safe method of therapy for older children and adolescents, as with adults, to treat hyperthyroidism of Graves disease (Graves-Basedow disease). The use of radioiodine as initial therapy or, as more often, the second line of therapy following antithyroid drug treatment is highly efficacious and rarely associated with short-term or long-term side effects. The indications for radioiodine therapy are failure of antithyroid drug therapy, idiosyncratic hypersensitivity reactions to antithyroid drugs, contraindications for surgical therapy including patients who refuse surgery, and the desirability to permanently prevent the development of hyperthyroidism. The treatment will induce permanent primary hypothyroidism within months after the use of ablative doses of radioiodine. The safety and simplicity of clinical management with L-thyroxine therapy for hypothyroidism favor radioiodine therapy for Graves disease over the potential risks from treatment with antithyroid drugs or surgery, and from untreated or relapsing hyperthyroidism. Radioiodine therapy is associated with the lowest morbidity and mortality among the currently available methods of therapy for Graves disease.