[en] The application of nuclides for therapy is a noninvasive treatment modality, which is characterized by the selective delivery of the radiation dose to target tissues (tumors or organs). Radionuclide therapy provides an alternative to surgical or medical treatment for several benign disorders. Basically, it is disease (metabolic radionuclide therapy). On the same principle is based the nuclide therapy of any endocrine tumors. The paper presents several methods for determination of the dose in treatment of thyroid diseases. A data of the '1'3'1' I therapy of thyroid diseases at the Medical University of Sofia are shown