Background Infants <32 weeks’ gestation should not be exposed to topical iodine and its avoidance is recommended during pregnancy and breast feeding. Exposure to contrast media and topical iodine are frequently used in many preterm neonates.Aim To determine whether thyrotropin levels in preterm infants are affected by exposure to intrapartum/neonatal topical iodine and/or use of iodinated contrast media.Design Infants <32 weeks’ gestation were recruited. Maternal and neonatal exposure to iodinated contrast media and topical iodine was recorded; levels of thyrotropin and thyroxine were measured from blood-spot card on postnatal days 7, 14, 28 and the equivalent of 36 weeks’ gestation.Results 125 infants were exposed to topical iodine/contrast media and 48 infants were unexposed. No infants were treated for hypothyroidism; 3 infants (exposed group) had transient hyperthyrotropinaemia. Mean thyrotropin levels were significantly higher on postnatal days 7, 14 and 28 in infants exposed to topical iodine prior to caesarean section compared to unexposed infants; a relationship which persisted after adjustment.Conclusions In the context of this study neonatal thyroid dysfunction was seen following exposure to iodine via caesarean section but not via exposure to contrast media.