A decreased serum TSH level can be observed in more than 10% of the German population. Although treatment is not mandatory in each of these cases patients with an unrecognized autonomous thyroid dysfunction have a substantial risk of developing thyrotoxicosis when exposed to large amounts of iodine. Thionamid drugs in combination with potassium perchlorate are given for preventive and therapeutic reasons until definitive thyroidectomy or radioiodine therapy is performed. In younger patients Graves' disease is the main cause of hyperthyroidism. Medical treatment with antithyroid drugs is established to render patients euthyroid. Having decreased the dose as far as possible, drug therapy is continued for 12-18 months to achieve a maximum rate of permanent remission. Ongoing clinical research aims to characterize clinical or laboratory predictors associated with a high risk of relapse after medication is stopped. Selenium supplementation is proposed to be a new therapeutic approach for autoimmune thyroid disease. It is already used quite liberally although data of powerful randomized trials are not available.