--- - |2 Abstract The consequences of lead exposure for later crime are theoretically compelling, but direct evidence from representative, longitudinal samples is sparse. By capitalizing on an original follow‐up of more than 200 infants from the birth cohort of the Project on Human Development in Chicago Neighborhoods matched to their blood lead levels from around age 3 years, we provide several tests. Through the use of four waves of longitudinal data that include measures of individual development, family background, and structural inequalities in how lead becomes embodied, we assess the hypothesized link between early childhood lead poisoning and both parent‐reported delinquent behavior and official arrest in late adolescence. We also test for mediating developmental processes of impulsivity and anxiety or depression. The results from multiple analytic strategies that make different assumptions reveal a plausibly causal effect of childhood lead exposure on adolescent delinquent behavior but no direct link to arrests. The results underscore lead exposure as a trigger for poisoned development in the early life course and call for greater integration of the environment into theories of individual differences in criminal behavior. - Criminology, Volume 56, Issue 2, Page 269-301, May 2018.