Prenatal exposure to tobacco smoke is a major risk factor associated with Sudden Infant Death Syndrome (SIDS) and the risk has increased despite continued advice against this practice. Evidence from the UK suggests the prevalence of maternal smoking during pregnancy has risen amongst SIDS mothers (from 50% to 80%) when the rate amongst expectant mothers in the general population has fallen (from 30% to 20%) confirming pooled estimates from recent studies of a four-fold risk. An additional risk from postnatal exposure has also been identified; increasing with the number of smokers in the household or the daily hours the infant is subjected to a smoke-filled environment. Exposure may lead to a complex range of effects upon normal physiological and anatomical development in fetal and postnatal life that places infants at greatly increased risk of SIDS. Recent legislation prohibiting smoking in public places needs to emphasise the adverse effects of tobacco smoke exposure to infants and amongst pregnant women.