This study sought to identify differences within injection drug using (IDU) couples in reporting of sexual and needle risk behavior. Subjects were thirty-nine heterosexual couples entering methadone maintenance. In 33.3% of couples, one member reported sharing needles while the other member reported no sharing. In 12.9% of couples, one member reported sharing injection equipment, while the other member reported no sharing. Agreement was 77.4% between members of monogamous couples regarding frequency of condom use, 80.7% regarding vaginal intercourse with condoms, and 25.8% regarding vaginal intercourse without condoms. Within couples, a number of differences between members of the couple in injection equipment sharing were noted, suggesting that individuals who attempt to protect themselves by not sharing injection equipment may be placed at risk by their sexual partners. Further clinical and research efforts should be directed toward reducing barriers to behavior that would protect both partners. Implications for self-report measurement of HIV risk behavior and for preventive interventions are discussed.