AIM To assess the effectiveness of a sexual risk reduction intervention in the Russian narcology hospital setting. DESIGN, SETTING AND PARTICIPANTS This was a randomized controlled trial from October 2004 to December 2005 among patients with alcohol and/or heroin dependence from two narcology hospitals in St Petersburg, Russia. INTERVENTION Intervention subjects received two personalized sexual behavior counseling sessions plus three telephone booster sessions. Control subjects received usual addiction treatment, which did not include sexual behavior counseling. All received a research assessment and condoms at baseline. MEASUREMENTS Primary outcomes were percentage of safe sex episodes (number of times condoms were used / by number of sexual episodes) and no unprotected sex (100% condom use or abstinence) during the previous 3 months, assessed at 6 months. FINDINGS Intervention subjects reported higher median percentage of safe sex episodes (unadjusted median difference 12.7%; P = 0.01; adjusted median difference 23%, P = 0.07); a significant difference was not detected for the outcome no unprotected sex in the past 3 months [unadjusted odds ratio (OR) 1.6, 95% confidence interval (CI) 0.8-3.1; adjusted OR 1.5, 95% CI 0.7-3.3]. CONCLUSIONS Among Russian substance-dependent individuals, sexual behavior counseling during addiction treatment should be considered as one potential component of efforts to decrease risky sexual behaviors in this HIV at-risk population.