Previous investigations have shown that women exposed to polychlorinated biphenyls (PCBs) are at increased risk of giving birth to an infant with low birth weight (< 2,500 g), and that this relationship is stronger for male than for female infants. We have tested the hypothesis that residents in a zip code that contains a PCB hazardous waste site or abuts a body of water contaminated with PCBs are at increased risk of giving birth to a low-birth-weight baby. We used the birth registry of the New York State Vital Statistics to identify all births between 1994 and 2000 in New York State except for New York City. This registry provides information on the infant, mother, and father together with the zip code of the mother's residence. The 865 state Superfund sites, the 86 National Priority List sites, and the six Areas of Concern in New York were characterized regarding whether or not they contain PCBs as a major contaminant. We identified 187 zip codes containing or abutting PCB-contaminated sites, and these zip codes were the residences of 24.5% of the 945,077 births. The birth weight in the PCB zip codes was on average 21.6 g less than in other zip codes (p < 0.001). Because there are many other risk factors for low birth weight, we have adjusted for these using a logistic regression model for these confounders. After adjusting for sex of the infant, mother's age, race, weight, height, education, income, marital status, and smoking, there was still a statistically significant 6% increased risk of giving birth to a male infant of low birth weight. These observations support the hypothesis that living in a zip code near a PCB-contaminated site poses a risk of exposure and giving birth to an infant of low birth weight.