INTRODUCTION: Understanding the role of opiate dependency treatment in risky sexual behavior could help optimize interventions for people who inject drugs (PWID). OBJECTIVES: We evaluated whether long-term medication-assisted treatment (LT-MAT) of opiate dependency with buprenorphine/naloxone influenced risky sexual behavior among HIV-uninfected PWID and identified predictors of risky sexual behavior. METHODS: We used data from HPTN 058, a randomized controlled trial of LT-MAT vs. short-term medication-assisted treatment among PWID in China and Thailand. We evaluated associations between randomized opiate dependency treatment group and self-reported risky sexual behaviors within the past month: condomless sex with primary partner, condomless sex with nonprimary partner, multiple partners, and more than 3 sexual acts. We used generalized estimating equations to conduct intention-to-treat, as-treated, and exploratory analyses of these associations. RESULTS: Of 1250 participants included in the analysis, 92% were male, with median age of 34 years (interquartile range 28-39). At baseline, referring to the past month, 36% of participants reported condomless sex with primary partner, 4% reported condomless sex with nonprimary partner, 6% reported multiple sex partners, and 30% reported more than 3 sexual acts. Risky sexual behaviors did not differ significantly between treatment groups at any point. Significant predictors (P < 0.05) of condomless sex with nonprimary partner were history of incarceration and noninjection drug use. Number of needle-sharing partners, noninjection drug use, and higher income were predictors for multiple sexual partners. CONCLUSIONS: LT-MAT did not significantly modify risky sexual behavior among HIV-uninfected PWID. Interventions that reduce sexual risk should target PWID with history of incarceration, alcohol use, and needle sharing.