Endometriosis is associated with a chronic local inflammatory process and the presence of autoantibodies, and these are characteristics of other autoimmune diseases.4–6 In addition, the thyroid peroxidase antibody is more highly expressed in patients with endometriosis than in patients without endometriosis.7 These findings suggest that endometriosis and autoimmune thyroid diseases might be associated. The gene discussed is TPO; the disease is endometriosis.