HIV-positive injection drug users (IDUs) ( N = 161) were recruited to complete a qualitative interview and a quantitative survey about sexual behavior and transmission risk. We identified two contexts in which exposure encounters occurred most commonly for HIV-positive IDUs: in intimate serodiscordant relationships and in the drug/sex economy. Salient characteristics in both contexts included the role of intimacy, drug use and sexual decision making, disclosure of HIV status, and perceived responsibility. Although these characteristics emerged in both risk contexts, they operated differently within each context. The preservation of intimacy was paramount among those in serodiscordant relationships, and agreements to take risks were common. In the drug/sex economy, serostatus disclosure was uncommon and drug acquisition and use played a significant role in sexual risk taking. Our data emphasize a need to address the specific transmission risk contexts occurring among HIV-positive IDUs and to prioritize social and interpersonal factors when promoting safer sexual norms among HIV-positive IDUs.