Narcotic abuse having premarital sexual intercourse and multiple sexual partners is risky behavior. Problems caused by narcotic abuse are very complex, such as social and health problems. Tendency of narcotic users committing early and unsafe sexual intercourse worsen condition of the addict's quality of life and definitely has a big impact on life survival in the future. This study aimed to determine determinants of risky sexual behavior among narcotic users. The method was cross sectional study using secondary data of medical record assessment at Medical Psikiatric Evaluation installation in Jakarta hospital for drug addicts in 2013. The study population was narcotic-addicted patients hospitalized at Cibubur Hospital for Drug Addicts within 2013. Sample of this study was all hospitalized patients amounted to 74 respondents. Data analysis used was univariate, bivariate and multivariate analysis. Results proved that most respondents had committed risky sexual behaviors worth 82.4% in which the age of first intercourse ≤ 17 years old worth 78.4%. The age of first intercourse ≤ 17 years old was the most influential variable to risky sexual behavior among narcotic addicts. The final model of multivariate analysis showed that narcotic users who committed sexual intercourse ≤ 17 years had 6.74 times opportunity (CI = 1.84 – 24.73) to commit risky sexual behavior than > 17 yearold narcotic users.