The role of peers in fostering deviant behavior in adolescence is well-documented in the sociological literature, while support for parental influence or "control" theories of deviance is more equivocal. This paper examines the relative influences of parents and peers on adolescent delinquency and marijuana use, using data from a three-wave panel study of youths who were paired with a best friend (N = 435). Covariance structure models based upon polychoric correlations among study variables reveal that friends are indeed the primary source of influence on youths' behavior, but that estimates of influence are grossly overstated in analyses relying upon respondents' perceptions of their friends' behavior. Parental supervision and attachment are weakly related to subsequent delinquency and marijuana use, lending little support to control theories of deviance. Findings reveal that different processes account for the similarities among members of delinquent and drug-using peer groups. Although youths are socialized into delinquent behavior by peers, both selection and socialization influences play important roles in the formation of drug-using peer groups.