Objective: Juvenile offenders report high rates of sexual risk taking, increasing the possibility of HIV. This 2-arm group randomized controlled trial tested the efficacy of PHAT Life, a sexual risk reduction program, compared with a time-matched health promotion program for youth on probation. Method: Male and female 13- to 17-year-olds (M = 16.08; SD = 1.09) recently arrested and placed on probation at an Evening Reporting Center were eligible for the study. Youth were 66% male, and 90% African American. Teens self-reported their sexual behavior (condom use, number of sexual partners) at baseline and 6 months. Retention was 85%. Results: Youth were randomized to PHAT Life (n = 163) or a health promotion program (n = 147). Among youth reporting the highest risk at baseline (a composite measure of multiple partners and inconsistent condom use), those who received PHAT Life were over 4 times more likely than the control group to report a lower level of risk (i.e., no sex or one partner plus consistent condom use) by 6 months, OR = 4.28 with 95% CI [1.37, 13.38], SE = 0.58, p = .01. Among sexually active teens who reported sexual debut before 12-years-old, those who received PHAT Life reported significantly fewer sexual partners at 6-months than controls, partial eta squared = .32, p = .002. Conclusions: Findings support PHAT Life’s efficacy to reduce sexual risk for juvenile offenders on probation. Future research should examine how best to disseminate PHAT Life to ensure that it is self-sustaining within the juvenile justice system.