The objective of this study was to determine whether women living in the vicinity of industrial districts where emission levels of air contaminants from multiple sources including petrochemical, petroleum, steel, and shipbuilding industries are highly correlated with increased incidence of preterm births. The prevalence of delivery of preterm-birth infants was significantly higher in mothers living in the industrial study area compared to control regions of Taiwan. After controlling for several possible confounders (including maternal age, season, marital status, maternal education, infant gender, and birthplace), the adjusted odds ratio was 1.11 (95% CI = 1.02-1.21) for delivery of preterm infants in the industrial area. Data provide further support for the hypothesis that air pollution can affect the outcome of pregnancy, although a semiecological study cannot confirm a direct causal relationship.