The present study (a) tests main and moderational effects of neighborhood and family risk, and adolescent impulsivity on the development of male and female antisocial behavior (ASB) and (b) examines the extent to which these effects work indirectly through parental knowledge. Adolescents (N = 4,597; 51% male) reported on informal social control in their neighborhoods, their family types, and impulsivity at age 12, and on parental monitoring and ASB at ages 13 and 15 years. Neighborhoods were further defined as risk and nonrisk in economic deprivation by census-level data. Main effects of neighborhood risk, single parenthood, and impulsivity on ASB were found for male and female adolescents. For female adolescents, impulsivity interacted with neighborhood economic deprivation and with family type in the prediction of parental knowledge. Impulsivity and contextual risk factors in part increased adolescent ASB through decreasing parental knowledge. Theoretical and policy implications are discussed. © 2010 American Psychological Association.