Hashimoto's thyroiditis, also known as chronic lymphocytic thyroiditis, is the primary cause of hypothyroidism. The development of Hashimoto's thyroiditis is closely linked to genetic factors and autoimmune abnormalities caused by disorders in iodine metabolism. The clinical manifestations of Hashimoto's thyroiditis vary, with the typical presentation being a diffuse, firm, painless, mild to moderate enlargement of the thyroid gland. Symptoms of compression in the neck and systemic symptoms are usually not prominent. Thyroid function may be normal or reduced, but thyroid autoantibodies such as thyroglobulin antibodies, thyroid peroxidase antibodies, and thyroid-stimulating hormone antibodies are often present in the bloodstream. Patients with Hashimoto's thyroiditis often have a family history of autoimmune diseases.