Polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDT) are persistent, bioaccumulative and toxic pollutants which were broadly used in the US until the 1970s. Common exposure to PCBs, DDT, and dichlorodiphenyldichloroethylene (DDE), the most stable metabolite of DDT, may influence children's neurodevelopment and growth, but study results are not consistent. This dissertation reported the concentrations of PCBs, DDT and DDE in breast milk of lactating women in Central North Carolina in 2004-2006, and examined the associations between lactational exposure to PCBs, DDT and DDE and infant development and growth at 12 months using data from the Pregnancy, Infection and Nutrition Babies Study, 2004-2006. PCBs, DDT and DDE were measured in breast milk at the third month postpartum. Lactational exposure of these chemicals was estimated by the product of chemical concentrations and the duration of breast feeding. Infant development at 12 months was measured by the Mullen Scales of Early Learning (n=231) and the Short Form: Level I (infant) of the MacArthur-Bates Communicative Development Indices (CDI) (n=218). Serial infant growth measurements through the first 12 months of life were regularly recorded in each child's growth card by pediatric practitioners (n=206). No consistent associations were observed between lactational exposure to PCBs, DDT and DDE through the first 12 months and the measures of infant development. However, DDE was associated with scoring below average on the gross motor scale of the Mullen among males only (adjusted OR=1.9, 95%CI=1.1, 3.3). Among infants breast fed for 6 months or longer there was no difference in weight and length through the first 6 months as the concentrations of PCBs, DDT and DDE increased. No difference was observed in weight and length at 12 months when comparing the accumulated lactational exposure through 12 months after controlling for total duration of breast feeding. In the ranges of chemical concentrations studied here, combined with the beneficial effects of the long duration of breastfeeding in this study population, lactational exposure to PCBs, DDT and DDE did not appear to impair infant neurodevelopment at 12 months, and resulted in no negative influence on infant growth in the first 12 months.