The promotion of supine sleeping position in young infants has resulted in significant declines in the incidence of Sudden Infant Death Syndrome although little is understood in terms of mechanisms. We hypothesize that supine sleeping position promotes appropriate thermal regulation via the face and head which is the major source of infant heat loss. By facilitating temperature regulation, the supine position ensures that the centre for thermoregulation in the hypothalamus does not become dysfunctional due to local temperature fluctuations. Because these hypothalamic, thermoregulatory neurones are synaptically linked to those regulating respiration in the medulla, adequate temperature control by the infant maintains normal respiration. In contrast, an increase in face and head temperature over and above core temperature would suggest thermoregulatory stress and an increased likelihood of respiratory apnoea.