Thyroid gland has the unique ability to concentrate iodine. This phenomenon offers a perfect background for a wide range of diagnostic tests utilizing radioactive iodine nuclides of iodine and technetium. Despite the very good availability of ultrasonography and other imaging modalities, radionuclide methods are still inevitable in a various cases of thyroid disease. In this article, a comprehensive review of all these methods used in the diagnosis of benign thyroid diseases is presented. Iodine and technetium uptake tests are briefly described. Indications to thyroid scan in the context of iodine supply are also presented. Finally, the significance of thyroid findings in PET images is pointed out. The article is illustrated by some typical patterns of radionuclide thyroid images.