Iodine is the most important trace element in the human body. Its main function is to participate in the synthesis of thyroid hormones, thyroxine (T4) and triiodothyronine (T3). The main source of iodine for humans is food rich in this trace element. The iodine content in foods varies greatly. The main sources of iodine are seafood, iodized salt, seaweed, as well as dairy products and egg yolks. In addition, iodine is found in a number of drugs for external and internal use, dietary supplements, and in iodinated contrast agents.Low-iodine diet (less than 50 μg per day) is prescribed before radioactive iodine therapy (RAIT) for thyroid diseases, namely hyperthyroidism and differentiated thyroid cancer. Currently, there is no consensus on the clinical benefits of such a diet, especially in countries with iodine deficiency, such as Russia.The aim of this review is to assess the need for a low-iodine diet and its optimal duration, as well as to determine the clinical characteristics affecting the outcome of RAIT, based on data from recent studies.