Hyperthyroidism is mainly caused by Graves' disease and toxic adenoma or multinodular goiter. In Europe, treatment of both disorders is usually started with antithyroidal drugs such as methimazole. Complications include agranulocytosis and the risk is dose-dependent. The starting dose of methimazole should not exceed 15-20 mg/d. Propylthiouracil can cause severe liver failure, leading to liver transplantation or death. Propylthiouracil, therefore, should not be used as first line agent and is only recommended when an antithyroid drug is to be started during the first trimester of pregnancy or in individuals who have experienced adverse responses to methimazole. Toxic adenoma is finally treated with radioioidine. To reduce the risk of treatment failure, antithyroidal drugs should be stopped at least one week prior to radioiodine. For Graves' disease, remission is unlikely if antibodies against the TSH-receptor remain above 10 mU/l after 6 months of antithyroidal treatment and radioiodine or thyroidectomy can be recommended. Thyroidectomy should be performed as (near) total thyreoidectomy.