Previous research has suggested that infertility is closely associated with hypothyroidism. However, the incidence of hypothyroidism in infertile women is estimated to be less than 1%, and many clinicians question the value of including routine screening for hypothyroidism as part of the infertility assessment. The frequency of increased thyroid stimulating hormone (TSH) in patients with a history of infertility seen at reproductive endocrinology and infertility centers was investigated.