Methadone maintenance programs (MMP) have the potential to play an important role in reducing HIV risk, given the appropriate type and level of ancillary treatments. In this study, we investigated the efficacy of a 12-session harm reduction group intervention for injection drug users, based upon the Information-Motivation-Behavioral skills model of behavior change, that focused on reducing both drug and sex risk. Two hundred and twenty patients entering an MMP were randomized to receive either standard care (SC)-2 hours of counseling per month and a single-session risk reduction intervention-or SC plus the harm reduction group (HRG). Results showed that during treatment, patients receiving HRG were more likely to be abstinent from cocaine and to report fewer unsafe sexual practices. Post-treatment, HRG patients scored higher on a sexual risk quiz and reported increased self-efficacy in high risk sexual situations. Enhancing methadone maintenance with a weekly harm reduction group treatment was somewhat more expensive but can bring about positive changes in behaviors and attitudes that are associated with the transmission of HIV.