Thyrotoxicosis most frequently is caused by Graves' disease and toxic adenoma. Author considers the difficulties of the diagnosis of these disorders. He established the prevalence and incidence of Graves' disease and toxic adenoma: 7.64% and 16.3/10(5)/year in the former and 2.34% and 4.1/10(5)/year in the later. The rate of the prevalence of these disorders in similar to that of iodine deficiency areas thus it refers indirectly to the deficiency of iodine in Hungary. The author suggests to determine correctly the nature of toxic multinodular goiter (autoimmune phenomenon or a variety of autonomous function) because it may have some importance in respect of therapy.