Although the rate of sudden infant death syndrome (SIDS) has been reduced with the 'Back to Sleep' campaign, SIDS is still a common cause of death in infancy. A range of environmental factors may interact to contribute to the adverse health conditions conducive to SIDS. Nine studies have evaluated the association between exposure to air pollution and the incidence of SIDS. The available evidence is inadequate to come to any conclusion about a relationship between air pollution and SIDS, although the body of evidence appears to suggest that air pollution (especially particles and some gaseous pollutants) may play a certain role in the occurrence of SIDS. We suggest that future studies should focus on the research design, role of indoor air quality and the effect of smaller particles, particularly those in the ultrafine range.