In this study, we aim to retrospectively measure the levels of DNA repair proteins (MSH2, MLH1, and MGMT) from representative blocks of tissue material in patients with a confirmed diagnosis of papillary thyroid carcinoma, chronic thyroiditis, or nodular colloidal goiter by thyroidectomy and to examine the clinical predictive effect of these levels. The gene discussed is MGMT; the disease is Hashimoto thyroiditis.