The petrochemical industry is the main source of industrial air pollution in Taiwan. To date, little is known about the possible effects of such pollution on the human fetus. In this study, the authors investigated the relationship between term low birthweight and preterm delivery and residence in a petrochemical industrial municipality (PIM). The study areas included 16 PIMs (which were defined as municipalities in which the number of workers in the petroleum and petrochemical industry made up at least 2% of the municipality's total population) and 16 matched reference municipalities (RFMs). Among 39,750 1st-parity singleton live births, the prevalences of preterm delivery in the PIMs and RFMs were 4.72% and 4.58%, respectively, and the prevalences of term low birthweight were 2.51% and 2.35%, respectively. When PIMs were compared with RFMs, and after controlling for possible confounders (including maternal age, marital status, maternal education, and gender of the baby), the adjusted odds ratios were 1.07 (95% confidence interval [CI] = 0.95, 1.22) for term low birthweight and 1.03 (95% CI = 0.94, 1.13) for preterm delivery, respectively.