Although the well-documented association between parental divorce and adolescent delinquency is generally assumed to be environmental (i.e., causal) in origin, genetic mediation is also possible. Namely, the behavior problems often found in children of divorce could derive from similar pathology in the parents, pathology that is both heritable and increases the risk that the parent will experience divorce. To test these alternative hypotheses, the authors made use of a novel design that incorporated timing of divorce in a sample of 610 adoptive and biological families. They reasoned that if genes common to parent and child mediate this association, nonadopted youth should manifest increased delinquency in the presence of parental divorce even if the divorce preceded their birth (i.e., was from a prior parental relationship). However, should the association be environmental in origin, the authors reasoned that adolescents should manifest increased delinquency only in response to divorce exposure, and this association should not vary by adoption status. Results firmly supported the latter, suggesting that it is the experience of parental divorce, and not common genes, that drives the association between divorce and adolescent delinquency.