After being in a relatively stable thermoneutral uterus for the whole of pregnancy, the newborn baby enters a cooling environment and might suffer significant heat loss and hypothermia in the first minutes of life. Alternatively, the fetus might face significant hyperthermia during and immediately after delivery if the mother is febrile. Hypothermia, particularly in preterm babies, is associated with increased morbidity and mortality. Hyperthermic babies have a worse short-term outcome, and hyperthermia can be particularly detrimental in association with intrapartum asphyxia and infection. Prevention and treatment of these variations in temperature are still developing and the efficacy of some strategies remains unclear. Nevertheless, one goal in the delivery room is to maintain the newborn baby's temperature within the physiologically optimum range.