The present study characterized prototypical patterns of development in self-reported externalizing behavior, between 12 and 22 years of age, within a community sample of 452 genotyped individuals. A Caucasian subset (n = 378) was then examined to determine whether their probabilities of displaying discrete trajectories were differentially associated with "CHRM2," a gene implicated in self-regulatory processes across a range of externalizing behaviors, and if affiliating with antisocial peers moderated these associations. Findings indicate that relative to a normative "lower risk" externalizing trajectory, likelihood of membership in two "higher risk" trajectories increased with each additional copy of the minor allelic variant at "CHRM2," and that this association was exacerbated among those exposed to higher levels of peer group antisocial behavior.