Recently, there were reports about the involvement of selenium deficiency in the development of autoimmune thyroiditis. A clinical study of the effect of the fixed combination of 150 µg of iodine and 75 µg of selenium has been carried out. It was found that after six months of therapy the concentration of free thyroxine significantly increases and the concentration of antibodies to peroxidase decreases. A comparison with the group of monotherapy using iodine 150 µg/day also showed a significant difference according to peroxidase antibodies concentration in favor of administration of iodine and selenium combination. Increased levels of free thyroxine, along with a trend towards thyroid stimulating hormone decrease, can be considered as a possible positive effect of the fixed combination of iodine and selenium (IoSen®) on the functional status of the thyroid gland. This effect was found for the first time and requires further study.