The control of ventilation is accomplished in response to central and peripheral changes in the partial pressure of oxygen and carbon dioxide. In prematurely born infants the control of ventilation is immature, and this constitutes the physiological basis of apnoea of prematurity which is of mixed central and obstructive aetiology. Impaired control of respiration is implicated in the pathophysiology of the sudden infant death syndrome which is the unexplained and devastating death of an infant under one year of age, usually during sleep.