While most studies of AIDS risk behavior rely on self-reports, few studies have assessed the reliability of these reports. The present study examines self-reports of drug-related and sexual risk behavior among pairs of injecting drug users (IDUs) recruited from the streets in New York City. Since both members of the pair were interviewed, it was possible to compare their responses in order to assess reliability. Subjects reported on their contacts' demographic data (age, gender, race/ethnicity) and on shared risk behaviors, including syringe sharing. Despite the private and/or illegal nature of AIDS risk behaviors, IDU subjects were generally reliable in their reports of both demographic and AIDS risk behaviors.