Selenium (Se) is an important element that exerts its effects on the selenoproteins. It is an essential component of the glutathione peroxidase enzymes, which have anti-oxidant and anti-inflammatory properties, and a component of iodothyronine selenodeiodinases, which catalyze the extrathyroid production of T3 from T4. Se is important to several aspects of thyroid homeostasis and may influence the natural course of thyroid diseases such as autoimmune thyroiditis (AIT). This review analyzes the effects of Se supplementation in patients with AIT, based on the studies published on this issue to date.