Youth involved in the juvenile justice system are at elevated risk for HIV as a result of high rates of sexual risk taking, substance use, mental health problems and sexually transmitted infections. Yet few HIV prevention programs exist for young offenders. This pilot study examined change in juvenile offenders’ sexual activity, drug/alcohol use, HIV testing and counseling, and theoretical mediators of risk taking following participation in preventing HIV/AIDS among teens (PHAT Life), an HIV-prevention program for teens on probation. Participants (N = 54) were 13–17 year-old arrested males and females remanded to a detention alternative setting. Youth participated in a uniquely tailored HIV prevention intervention and completed a baseline and 3-month follow up assessment of their HIV and substance use knowledge, attitudes, beliefs, and behaviors. At 3-month follow up, teens reported less alcohol use, more positive attitudes toward peers with HIV, greater ability to resist temptation to use substances, and for males, improved HIV prevention self-efficacy and peer norms supporting prevention. Teens were also more likely to seek HIV counseling and males were more likely to get tested for HIV. Effect sizes revealed moderate change in sexual behavior. Findings support PHAT Life as a promising intervention to reduce HIV-risk among youth in juvenile justice.