In dizygotic premature twins delivered by Caesarean section after prolonged efforts to effect premature birth we found markedly enhanced thyroid stimulating hormone levels. The mother had been subjected to local polyvidone iodine therapy for seven weeks with PVP suppositories to prevent vaginal infections. Control checks revealed persistently elevated TSH levels, whereas T3/T4 levels were always reduced. Greatly pronounced iodine excretion was seen in the urine of both the babies. This raised the suspicion of iodine-induced hypothyroidism in both children. Substitution with 1-thyroxine was initiated and a withdrawal trial performed after 12 weeks. The patients remained euthyroid after the treatment had been discontinued. Due to possible transfer of iodide to the fetus associated with the risk of iodine-induced hypothyroidism, it is recommended to abstain from vaginal application of iodine during pregnancy.