Vitamin D receptors exist in many body organs. Through these receptors, vitamin D has various functions, including the regulation of ion homeostasis, cell growth, cell differentiation, and cellular immunity [
1]. Vitamin D plays an important role in preventing the occurrence of many inflammatory diseases, infections, and autoimmune diseases [
2]. In numerous studies, the relationship between vitamin D deficiency and a variety of diseases, including musculoskeletal [
3], cardiovascular [
4], kidney disease [
5], diabetes [
6] and infections [
7] had been shown. The thyroid gland is also one of the organs that have a receptor for vitamin D. The vitamin D receptor in the thyroid is a member of a large group of receptors called nuclear receptors, which also belong to the thyroid hormones receptor [
8]. Some studies indicated that vitamin D deficiency is associated with various autoimmune diseases [
9]. Today, Hashimoto is one of the most common acquired hypothyroidism and autoimmune disease in children and adults [
10]. The onset of autoimmune-thyroid disease with vitamin D deficiency is very common [
11]. Plenty of evidence has shown the role of vitamin D in the regulation of pro-inflammatory cytokines, regulatory T cell, and immune response [
12]. It seems that vitamin D deficiency leads to an increase in the risk of autoimmune diseases. Vitamin D also can reduce the pathogenesis of DCs cells, macrophage, CD4 + T, CD8 + T, and B cells [
9]. Besides, it has been shown as a selective immune inhibitor that plays an important role in suppressing and preventing the development of autoimmune diseases such as encephalopathy, rheumatoid arthritis, systemic lupus erythematosus, diabetes type 1, and intestinal inflammatory diseases [
13‐
15]. Recent studies have shown the role of vitamin D deficiency in autoimmune thyroids, such as Hashimoto thyroiditis [
16,
17]. To the best of our knowledge, there is contradictory research about the relationship between thyroid diseases, especially hypothyroidism and vitamin D deficiency; therefore, in the present study, we aimed to evaluate the vitamin D level in hypothyroidism patients. Besides, there was no study comparing the vitamin D level in immune and non-immune hypothyroidism, and the relationship between the anti-TPO level and vitamin D, as well as the disease treatment status and vitamin D; hence, in the present study we evaluated the mentioned issues.