Thyroid dysfunction is extremely common in women and has unique consequences related to menstrual cyclicity and reproduction. Even minimal hypothyroidism can increase rates of miscarriage and fetal death and may also have adverse effects on later cognitive development of the offspring. Hyperthyroidism during pregnancy may also have adverse consequences. Accordingly, thyrotropin (TSH) determination is warranted for all women planning pregnancy or those already pregnant. Replacement doses should be carefully monitored throughout pregnancy because the increased renal iodine loss and estrogen-induced rise in thyroxine-binding globulin (TBG) often result in a higher dose requirement. Although thyroid abnormalities are part of the standard differential diagnosis of menstrual disorders, recent studies indicate that these are relatively infrequent causes. Nonetheless, TSH is still required as part of the laboratory evaluation of women with abnormal cycles. The incidence of postpartum thyroiditis is high--6%-8% in various studies. A TSH should be performed in all postpartum patients who are depressed, who complain of unusual fatigue or anxiety or have any of the classical symptoms of hyperthyroidism or hypothyroidism. Practitioners providing health care for women should be alert to thyroid disorders as possible etiological factors in nonspecific symptoms such as fatigue and depression. However, most women with these symptoms are euthyroid; replacement therapy for them is not indicated. The long-standing dogma of thyroidology that replacement with levothyroxine alone is satisfactory for all hypothyroid patients has recently been questioned but results of trials are inconclusive. Nonetheless, satisfactory regimens can be found for the vast majority of patients.