Autoimmune thyroiditis is an organ-specific autoimmune disease caused by the activation of self-reactive CD4+ T cells. Regulatory T (Treg) cells are a population of T cells that play a central role in immunological tolerance by suppressing selfreactive cells. CD4+ Tregs are divided into thymic (tTreg) and peripheral (pTreg). tTregs perform their functions through cytokine-independent mechanisms, pTregs – through IL-10, TGF-β and IL-35. Tregs perform a protective function against AIT. Studies of Treg level in AIT show different results, in most cases Treg level is increased, and their function is impaired. Treg function in AIT is affected by many factors, such as the level of thyroglobulin, vitamin D etc. Apart from the Treg level itself, the Th17/Treg ratio is also crucial in AIT. Activation of Tregs and modification of the Th17/Treg ratio can be used in AIT treatment.