Increased serum TGF-β concentrations have many consequences: suppression of the development of Graves’ disease; enhancement of the final pro-fibrotic stage of Hashimoto’s thyroiditis; exacerbation of fibrosis in thyroid-associated orbitopathy via enhanced maturation and differentiation of myofibroblasts, hyaluronan acid synthase activity, and cytokine synthesis; and suppression of autoimmune thyroid disease in pregnancy. The gene discussed is TGFB1; the disease is Hashimoto thyroiditis.