Fetal and neonatal autoimmune hyperthyroidism is a rare, serious but transient disorder. Early diagnosis and treatment are key objectives for an optimal prognosis and the well-being of the child. This review focuses on the management of these patients during the fetal and neonatal periods. We propose a diagnostic algorithm for high-risk pregnancies in mothers with current or past hyperthyroidism related to Graves' disease, involving repeated fetal thyroid gland assessments from 20 weeks of gestation onwards and maternal serum thyroid-stimulating hormone receptor antibody (TRAb) determination, with close monitoring if TRAb levels exceed 2 to 3 times the upper limit of the normal range. In fetuses with goiter, the main clinical issue is determining whether the cause is (1) maternal antithyroid drug (ATD) treatment that is appropriate for achieving normal maternal thyroid function but inappropriate and excessive for the fetus, resulting in hypothyroidism and necessitating a decrease in the ATD dose during pregnancy, or (2) the presence of TRAbs resulting in fetal thyroid stimulation and hyperthyroidism, requiring an increase in the maternal ATD dose. Methimazole/carbimazole treatment should be initiated as soon as possible during the neonatal period, carefully managed and maintained over a period of 1-3 months and then stopped when TRAb is no longer detectable in serum. (C) 2016 S. Karger AG, Basel