We present two cases of fetal hypothyroidism with goiter which were successfully diagnosed and treated in utero. In both cases, ultrasonographic examination demonstrated a bilobed solid anterior neck mass with increased vascularity compatible with enlarged thyroid gland. Fetal blood sampling revealed hypothyroidism. Intra-amniotic injection of L-thyroxin caused a reduction in thyroid gland size and enabled vaginal delivery without complication. In the first case, maternal thyroid hormone levels and autoantibodies were normal and the neonate had hypothyroidism suggesting the diagnosis of dyshormonogenesis. In the second case, the fetus had transient hypothyroidism, which resolved spontaneously after delivery. Maternal thyroid function tests and autoantibodies were normal and both the mother and neonate had normal urinary iodine, excluding the diagnosis of iodine deficiency or excess. Thus, we believe that transplacental transfer of undetermined factors might be a cause of transient congenital hypothyroidism. Also, we reviewed the literature and described controversial issues regarding the management of fetal goiter.