Overt hyperthyroidism is responsible for adverse obstetric and neonatal events including preeclampsia, congestive heart failure, preterm labor, stillbirth, and small for gestational age babies. On the other hand, women with hypothyroidism have a higher rate of spontaneous abortion, miscarriage, and anemia and are at increased risk for gestational hypertension, preeclampsia, placental abruption, postpartum hemorrhage, preterm delivery, low fetal birth weight, congenital malformations, fetal death, and neonatal respiratory distress. Therefore, Effective management of thyroid disease during pregnancy and the postpartum period is important for optimal maternal, fetal, and neonatal outcomes. The aims of this talk include (1) to review the changes in thyroid function during pregnancy; (2) to highlight the diagnosis and management of gestational hyperthyroidism and hypothyroidism; and (3) to provide the evidence clearly demonstrating that both overt hypothyroidism and hyperthyroidism should be treated. Controversy still exists regarding the treatment of subclinical hypothyroidism and thyroid antibody positive euthyroidism, and whether pregnant women should be screened for thyroid disease.