A wealth of empirical research has revealed that antisocial behavioral phenotypes result from genetic and environmental factors working independently and interactively. However, much of this research has focused on traditional forms of antisocial behavior, such as aggression and violence. At the same time, research has been slow to examine whether genetic factors may relate to involvement in fraudulent behaviors. This article addresses this gap in the literature and examines whether a polymorphism in the promoter region of the monoamine oxidase A (MAOA) gene interacts with exposure to delinquent peers to predict variation in fraudulent behaviors. Analysis of male participants from the National Longitudinal Study of Adolescent Health (J. R. Udry, 2003) revealed a statistically significant Gene x Environment interaction in which the high-MAOA activity allele increased the odds of fraudulent behaviors, but only among male participants with a high number of delinquent peers.