Viral respiratory infections are the most likely trigger for sudden infant death syndrome (SIDS). SIDS cases commonly have evidence of respiratory tract inflammation, a preceding history of symptoms of minor illness and occur in winter peaks coinciding with respiratory viral epidemics. Respiratory infections are a common cause for infants presenting with sudden events, involving apnoea and hypoxaemia and there are physiological mechanisms by which infants may develop sudden and severe, potentially life-threatening hypoxaemia. The rate of SIDS has fallen in the last 15 years. This is probably more to do with the reasons for the fall in deaths from respiratory causes rather than changes in sleeping position. Further falls in SIDS death rates may occur with reductions in cigarette smoking, encouragement of breastfeeding and minimising the potential for young infants to acquire respiratory infections. Early identification and recognition of life-threatening features of infections may further minimise the risks of sudden death.