Congenital hyperthyroidism is less frequent than congenital hypothyroidism but its impact on growth and development can be as dramatic. The immune form of hyperthyroidism that is transmitted from a mother with Graves’ disease to her foetus and then neonate is transient, but cases of persistent congenital hyperthyroidism had also been described, that can now be explained by molecular abnormalities of the thyrotropin receptor. The abundance of published data on the neonatal effects of maternal Graves’ disease contrasts with the paucity of information on fetal effects. Recent studies showed that it is of utmost to scrutinize fetal thyroid by expert ultrasonographist and to have a team work with obstetricians and pediatric endocrinologists in pregnant women with Graves’ disease. This allowed to accurately determine the fetal thyroid status and to adapt the treatment in the mothers successfully. Fetal hyperthyroidism does exist and needs an appropriate aggressive treatment. Clearly the fetus has become our patient!