Although there is widespread consensus that maternal smoking during pregnancy has adverse, long-term effects on neurobehavioral development in the offspring, it has been surprisingly difficult to prove that there are specific behavioral problems that can be incontrovertibly attributed to prenatal tobacco smoke exposure. It is now 16 years since a relationship was first postulated between maternal smoking and conduct disorder in the offspring,1 and in the intervening years, there have been numerous studies in support of a causal relationship, as well as studies claiming that other confounds obscure any role of tobacco. The article by Gaysina et al2 resolves this issue once and for all by examining the connection in 3 distinct, longitudinally followed up cohorts, incorporating not only the standard battery of covariables in such studies, but also involving genetically related and unrelated families with children raised by biological or adoptive parents. Therefore, their meta-analysis controls for perinatal and postnatal confounds including differences in child-rearing practices or the home environment. Thus, the conclusion is incontrovertible: prenatal tobacco smoke exposure contributes significantly to subsequent conduct disorder in the offspring. Considering the relationship of conduct problems to poor school performance, social isolation, and juvenile and adult incarceration, the negative impact on the affected individuals’ quality of life and, ultimately, on society as whole, cannot be underestimated.