Emerging evidence suggests that variants of specific genes may influence some youths to seek out or associate with antisocial peers. Using genotypic data (N = 1,816) from the National Longitudinal Study of Adolescent Health (J. R. Udry, 1998, 2003), the authors tested this possibility. They found that the 10R allele of the dopamine transporter (DAT1) gene was associated with self-reported delinquent peer affiliation for male adolescents from high-risk environments ([beta] range = 0.13-0.14) despite controlling for delinquent involvement, self-control, and drug and alcohol use. The authors discuss the importance of using a biosocial framework to examine issues related to adolescent development.