Thyrotoxicosis is a common disorder, especially in women. The most frequent cause is Graves' disease (autoimmune hyperthyroidism). Other important causes include toxic nodular hyperthyroidism, due to the presence of one or more autonomously functioning thyroid nodules, and thyroiditis caused by inflammation, which results in release of stored hormones. Antithyroid drugs are the usual initial treatment (thionamides such as carbimazole or its active metabolite methimazole are the drugs of choice). A prolonged course leads to remission of Graves' hyperthyroidism in about a third of cases. Because of the low remission rate in Graves' disease and the inability to cure toxic nodular hyperthyroidism with antithyroid drugs alone, radioiodine is increasingly used as first line therapy, and is the preferred choice for relapsed Graves' hyperthyroidism. Total thyroidectomy is an option in selected cases. Future efforts are likely to concentrate on novel and safe ways to modulate the underlying disease process rather than stopping excess thyroid hormone production.