Lead exposure is associated with low birth-weight. The objective of this study is to determine whether lead exposure is associated with lower body weight in children, adolescents and adults.We analyzed data from NHANES 1999–2006 for participants aged ≥3 using multiple logistic and multivariate linear regression. Using age- and sex-standardized BMI Z-scores, overweight and obese children (ages 3–19) were classified by BMI ≥85th and ≥95th percentiles, respectively. The adult population (age ≥20) was classified as overweight and obese with BMI measures of 25–29.9 and ≥30, respectively. Blood lead level (BLL) was categorized by weighted quartiles.Multivariate linear regressions revealed a lower BMI Z-score in children and adolescents when the highest lead quartile was compared to the lowest lead quartile (β (SE)=−0.33 (0.07), p<0.001), and a decreased BMI in adults (β (SE)=−2.58 (0.25), p<0.001). Multiple logistic analyses in children and adolescents found a negative association between BLL and the percentage of obese and overweight with BLL in the highest quartile compared to the lowest quartile (OR=0.42, 95% CI: 0.30–0.59; and OR=0.67, 95% CI: 0.52–0.88, respectively). Adults in the highest lead quartile were less likely to be obese (OR=0.42, 95% CI: 0.35–0.50) compared to those in the lowest lead quartile. Further analyses with blood lead as restricted cubic splines, confirmed the dose-relationship between blood lead and body weight outcomes.BLLs are associated with lower body mass index and obesity in children, adolescents and adults.