BACKGROUND The effects on postnatal growth of maternal exposure to low levels of lead during pregnancy have not been well established. In addition, information is limited regarding the protective effect of dietary calcium intake during pregnancy against the effect of lead for fetal and postnatal growth. We investigated the relationship between prenatal exposure to lead and growth at birth and 6, 12, and 24 months postnatal, and evaluated the role of calcium intake against the effect of lead. METHODS A total of 1150 pregnant women, and their subsequent offspring, enrolled in a prospective birth cohort study (Mothers and Children's Environmental Health Study), were evaluated. Multivariable regression analysis was conducted to estimate the effects of prenatal maternal blood lead levels on growth at each follow-up. RESULTS The blood lead levels of participating mothers were <5.0 μg/dL and mean levels were 1.25 μg/dL during the early (before 20 gestational weeks) and late (at delivery) gestational periods. Prenatal exposure to lead, particularly in late pregnancy, was significantly associated with a reduction in infantile growth at 24 months. When pregnant women had dietary calcium intake at mean or upper level, the association was not significant. In contrast, lower than mean level of calcium intake intensified the adverse effect of prenatal lead exposure on growth in children. CONCLUSIONS Prenatal lead exposure <5.0 μg/dL adversely affects postnatal growth and low calcium intake aggravates the effect, indicating more stringent control of lead and sufficient intake of calcium are necessary to help children's health.