Diffuse toxic goiter is a genetically determined autoimmune disease with a congenital defect of the immune system. With diffuse toxic goiter, the secretion of the thyroid hormones triiodothyronine (T3) and thyroxine (T4) increases, which often leads to thyrotoxicosis. Thyrotoxicosis is a clinical syndrome characterized by a persistent and prolonged increase in the level of thyroid hormones in the blood, which is caused by hyperstimulation of the thyroid gland by antibodies to the pituitary thyroid-stimulating hormone receptor. A characteristic sign of thyrotoxicosis is a significant increase in the level of basal metabolism with damage to all organs and systems [1,2,3]. The degree of proliferative activity of the follicular epithelium of the thyroid gland isimportant. Currently, to determine the degree of proliferation of the thyroid epithelium, an immunohistochemical research method is used [4,5]. Purpose of the study: to study the degree of proliferation of the follicular epithelium of the thyroid gland indiffuse toxic goiter.