Context. Contemporary threats to adolescents' health are primarily the consequence of risk behaviors and their related adverse outcomes. Identifying factors associated with adolescents' risk behaviors is critical for developing effective prevention strategies. A number of risk factors have been identified, including familial environment; however, few studies have examined the impact of parental monitoring. Objective. To examine the influence of less perceived parental monitoring on a spectrum of adolescent health-compromising behaviors and outcomes. Design. Survey. Setting. A family medicine clinic. Participants. To assess eligibility, recruiters screened a sample of 1130 teens residing in low-income neighborhoods. Adolescents were eligible if they were black females, between the ages of 14 and 18 years, sexually active in the previous 6 months, and provided written informed consent. Most teens (n = 609) were eligible, with 522 (85.7%) agreeing to participate. Main Outcome Measures. Variables in 6 domains were assessed, including: sexually transmitted diseases, sexual behaviors, marijuana use, alcohol use, antisocial behavior, and violence. Results. In logistic regression analyses, controlling for observed covariates, adolescents perceiving less parental monitoring were more likely to test positive for a sexually transmitted disease (odds ratio [OR]: 1.7), report not using a condom at last sexual intercourse (OR: 1.7), have multiple sexual partners in the past 6 months (OR: 2.0), have risky sex partners (OR: 1.5), have a new sex partner in the past 30 days (OR: 3.0), and not use any contraception during the last sexual intercourse episode (OR: 1.9). Furthermore, adolescents perceiving less parental monitoring were more likely to have a history of marijuana use and use marijuana more often in the past 30 days (OR: 2.3 and OR: 2.5, respectively); a history of alcohol use and greater alcohol consumption in the past 30 days (OR: 1.4 and OR: 1.9, respectively); have a history of arrest (OR: 2.1); and there was a trend toward having engaged in fights in the past 6 months (OR: 1.4). Conclusions. The findings demonstrate a consistent pattern of health risk behaviors and adverse biological outcomes associated with less perceived parental monitoring. Additional research needs to focus on developing theoretical models that help explain the influence of familial environment on adolescent health and develop and evaluate interventions to promote the health of adolescents.