Treatment of Graves' disease during pregnancy with antithyroid drugs (ATDs) poses a risk of inducing hypothyroidism and, thus, development of a goiter to the fetus. PATIENT FINDINGS: We report two patients referred to our department after discovery of a fetal goiter by ultrasound examination in the second trimester of pregnancy. The women receiving 400¿mg/day propylthiouracil and 10¿mg/day thiamizole, respectively, had thyrotropin and total thyroxine values within the normal reference range but a lowered free thyroxine level. Fetal blood sampling by cordocentesis revealed severe fetal hypothyroidism as the cause of goiter development. Reduction of maternal ATD dose and injection of levothyroxine intra-amniotically quickly reduced the goiter size, and both babies were born euthyroid and without goiters.