Risk factors for HIV infection were examined in 520 female sex partners (SPs) of injecting drug users (IDUs); 16% tested HIV positive (40% among former IDUs). In multivariate analyses, sex trade was associated with risk of HIV infection, whereas race, age, history of pneumonia or genital herpes, high self-rated AIDS risk, and IDU history were related to greater risk. Among women with no IDU history, cohabitation with a SP (not trading sex) predicted higher risk; having a female SP was also associated with higher risk. Secondary analyses suggest that total unprotected contacts with IDUs and both sex trade and cohabitation might account for these findings. The data suggest that, for female SPs of IDUs, reducing numbers of sex partners per se may not confer adequate protection from HIV. For women in committed relationships with IDUs, interventions should address contextual factors in relationships that elevate risk and complicate prevention.