Acute respiratory infections (ARIs) are the most common cause of illness and death in children in the developing world. This review focuses on outdoor air pollutants associated with pediatric ARI mortality and morbidity. Studies were identified using MEDLINE and other electronic databases. Four studies showed an increase in infant mortality in relation to outdoor air pollution. Short-term follow-up and time-series studies suggest that air pollutants act as risk factors for respiratory infection. Air pollution exposure increases the incidence of upper- and lower-respiratory infections in children. Because complex pollution mixtures are present in the studied urban areas, pollutant levels at which ARI risk would be expected to increase cannot be determined. Children may be at greater risk, given the poor environmental and nutritional conditions prevalent in developing countries.