We report a case of early diagnosis of iodide-induced fetal hypothyroidism at 22 weeks of gestation, confirmed at 29 weeks by cordocentesis and successfully treated intra-amniotically. The ultrasonographic feature was the presence of two echogenic masses in the fetal neck; polyhydramnios was absent. Mild hypothyroidism was diagnosed based on fetal serum obtained by percutaneous umbilical blood sampling at 29 weeks of gestation. The persistence of fetal hypothyroidism in spite of maternal thyroid improvement was confirmed by a second cordocentesis at 35 weeks of gestation, and a single injection of intra-amniotic levothyroxine (250 micrograms) was performed. The serial ultrasonographic examinations showed disappearance of the fetal goiter. A healthy female baby (3,630 g) was delivered at term. At birth, the thyroid gland was not enlarged, and neonatal thyroid hormones were within the normal range. This case suggests that cordocentesis is a reliable method to assess the fetal thyroid status; moreover a single injection of intra-amniotic thyroxine was effective in treating fetal hypothyroid goiter.