We analyzed the relationship of ethnicity and gender to high-risk sexual behavior among 457 male and female heterosexual intravenous drug users (IVDUs) interviewed in street and clinic settings in San Francisco. Over two-thirds said they never used condoms. More of the black respondents had not been enrolled in treatment. White IVDUs were more likely to report 10 or more partners, anal sex, and a steady drug-injecting partner; black respondents more often reported prostitution. More men said they never used condoms, and more women said they engaged in prostitution. These high-risk sexual behaviors were significantly and independently associated with ethnicity or gender when other sociodemographic variables were held constant. Sexual risk reduction for IVDUs, focusing on condom use, needs to be expanded to reach non-injecting partners. Intervention is critical for the black community, where a high proportion of IVDUs have steady non-injecting partners.