Outdoor air pollution, largely from fossil fuel burning, is a major cause of morbidity and mortality in the United States, costing billions of dollars every year in health care and loss of productivity. The developing fetus and young child are especially vulnerable to neurotoxicants, such as polycyclic aromatic hydrocarbons (PAH) released to ambient air by combustion of fossil fuel and other organic material. Low-income populations are disproportionately exposed to air pollution. On the basis of the results of a prospective cohort study in a low-income population inNew York City (NYC) that found a significant inverse association between child IQand prenatal exposure to airborne PAH, we estimated the increase in IQ and related lifetime earnings in a low-income urban population as a result of a hypothesizedmodest reduction of ambient PAH concentrations in NYC of 0.25 ng/m3. For reference, the current estimated annual mean PAH concentration is ~1 ng/m3. Restricting to NYC Medicaid births and using a 5 per cent discount rate, we estimated the gain in lifetime earnings due to IQ increase for a single year cohort to be US$215 million (best estimate). Using much more conservative assumptions, the estimate was $43 million. This analysis suggests that a modest reduction in ambient concentrations of PAH is associated with substantial economic benefits to children.