We present two cases of maternal Graves' disease complicated by fetal goitrous hypothyroidism. Both patients had elevated maternal thyroid-stimulating immunoglobulin and thyrotropic-binding inhibitory immunoglobulin antibody titers. Diagnosis of fetal hypothyroidism was made by cordocentesis, and serial injections of thyroxine into the amniotic fluid resulted in return to normal of fetal thyroid size and function at birth. Significance of in utero management of fetal hypothyroidism is discussed.