A structured interview was used to determine the details of high risk sexual behaviors, including number of sexual partners, frequency of condom use, and involvement in commercial sexual activity in 165 opioid abusers (mean age 34 years, 36% minority, 47% female) entering out-patient methadone substitution therapy. The median number of sexual partners in the sample was one, and 95% were sexually active in the past year. Most patients (84%) denied any commercial sexual activity and reported rates of monogamy and sexual abstinence (81%), and rates of condom use (15%), that were comparable with reports from general population surveys. However, intravenous drug abusers (IVDAs) remain at higher risk for exposure to HIV-1 because they are likelier to have sexual contact with other IVDAs and former IVDAs. Continuing efforts are needed to improve the safe sex practices of IVDAs, but it may be a significant challenge to reduce their high risk sexual behavior considerably below that of the general population. Concomitant drug abuse treatment may help in efforts to accomplish sexual behavior change.