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 is 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 the use of iodinated contrast media. Design: Infants <32 weeks' gestation were recruited. Maternal and neonatal exposures to iodinated contrast media and topical iodine were recorded; levels of thyrotropin and thyroxine were measured from blood-spot cards on postnatal days 7, 14, 28 and the equivalent of 36 weeks' gestation. Results: One hundred and twenty-five infants were exposed to topical iodine/contrast media and 48 infants were unexposed. No infants were treated for hypothyroidism; three infants (exposed group) had transient hyperthyro-tropinaemia. 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.