Building on social ecological research, this study considers whether neighborhood socioeconomic advantage modifies the relationship between parenting practices and sex initiation among young adolescents. Using data on a national sample of 2,559 middle school students, the authors examined two-way interactions between neighborhood socioeconomic status and parental involvement, decision making, and communication about sex. The parental decision-making measure was developed using latent class analysis. Greater parental involvement was related to a lower likelihood of sex initiation only when youth lived in socioeconomically advantaged neighborhoods. Parental decision making centered on the childs activities within (e.g., television watching) and outside (e.g., hanging with peers) of the home was associated with a lower likelihood of sex initiation for adolescents in disadvantaged neighborhoods but to a greater likelihood of sex initiation for youth in advantaged neighborhoods. Results suggest that the neighborhood context must be considered in preventive interventions aimed at discouraging adolescent involvement in sexual intercourse.