Results revealed that young boys who were exposed to prenatal smoking were significantly more likely than controls to develop ODD and comorbid ODD/ADHD, but were not more likely to develop ADHD alone. Exposed boys were also more likely to have an earlier onset of significant delinquent behavior and to have an increased risk of early onset of conduct problems. The conduct problems observed in exposed boys were characterized by socially resistant and impulsively aggressive behavior. The findings suggest that early intervention programs that target pregnant smokers and their young children may reduce the risk of early onset of delinquency and conduct problems. Participants were 448 boys from the youngest cohort of the Pittsburgh Youth Study, 37 percent of who were exposed to prenatal smoking. Variables under analysis included maternal smoking during pregnancy, conduct problems, ADHD, delinquent behavior, demographic information, single parent status, maternal education level, and other perinatal risk factors such as prenatal exposure to alcohol. Statistical data analysis included logistic regression and multinomial logistic regression analyses. Followup studies should consider the use of prospective exposure measures, such as biological assays. Tables, references