OBJECTIVES: We examined the effectiveness of risk reduction counseling and the role of on-site HIV testing in drug treatment. METHODS: Between January and May 2009, we randomized 1281 HIV-negative (or status unknown) adults who reported no past-year HIV testing to (1) referral for off-site HIV testing, (2) HIV risk-reduction counseling with on-site rapid HIV testing, or (3) verbal information about testing only with on-site rapid HIV testing. RESULTS: We defined 2 primary self-reported outcomes a priori: receipt of HIV test results and unprotected anal or vaginal intercourse episodes at 6-month follow-up. The combined on-site rapid testing participants received more HIV test results than off-site testing referral participants (P<.001; Mantel-Haenszel risk ratio=4.52; 97.5% confidence interval [CI]=3.57, 5.72). At 6 months, there were no significant differences in unprotected intercourse episodes between the combined on-site testing arms and the referral arm (P=.39; incidence rate ratio [IRR]=1.04; 97.5% CI=0.95, 1.14) or the 2 on-site testing arms (P=.81; IRR=1.03; 97.5% CI=0.84, 1.26). CONCLUSIONS: This study demonstrated on-site rapid HIV testing's value in drug treatment centers and found no additional benefit from HIV sexual risk-reduction counseling.