Hashimoto's thyroiditis (HT) is one of the most common autoimmune diseases associated with inflammation of the thyroid gland. Some fatty acids (FAs) are involved in inflammation. The aim of the study was to investigate how HT affects FA metabolism in thyroid tissue. We examined normal thyroid tissue from 92 patients with and without HT. We determined total FA panel, pro-inflammatory and specialized pro-resolving lipid mediators (SPMs) concentrations and measured the expression levels of genes encoding the corresponding enzymes of FA metabolism and mediator's synthesis. In HT tissue, we observed increased total lipid levels (p <
0.05), decreased carnitine palmitoyltransferase I (p <
0.05) and increased tumor necrosis factor alpha (p <
0.002) compared to healthy tissue. Simultaneously, we observed an overexpression of enzymes responsible for the synthesis of polyunsaturated FAs and their higher levels in HT tissue. However, despite the overexpression of phospholipase A