There were studied 46 patients with diabetes mellitus type 2 in order to identify the autoimmune processes directed against thyroid tissue and dependence of those changes on the level of leptin in blood serum. It was established that in patients with high leptin serum level antithyroid antibody titer increased. In order to adjust the levels of antithyroid antibodies sodium selenite was prescribed against the background of standard therapy. Statistically significant reduction in antibodies expression to thyroglobulin and thyroperoxidase after treatment with sodium selenite dosed 50 mg after a month has been found.