We examined sociodemographic, behavioral, and clinical characteristics associated with inconsistent condom use in a cross-sectional analysis of 145 sexually active HIV-serodiscordant heterosexual couples who participated in the California Partners Study II. All couples were aware of their HIV-serodiscordant status. Forty-five percent of couples reported having had unprotected vaginal or anal sex in the previous 6 months. In the multivariate couple-level analyses, factors independently associated with inconsistent (i.e., <100%) condom use in the previous 6 months included lower educational level, unemployment, African-American ethnicity, and practice of anal sex by the couple. Injection drug use was associated with inconsistent condom use among couples with younger HIV-infected partners. In addition, couples with HIV-infected partners who had higher CD4 cell counts and couples in which the HIV-infected male partner ever had sex with a man were more likely to use condoms inconsistently. Consistency of condom use did not depend on the gender of the HIV-infected partner or duration of sexual relationship. The findings suggest that many HIV-serodiscordant heterosexual couples remain at high risk of HIV transmission and may benefit not only from behavioral interventions but also from structural interventions aimed at improving their social and economic conditions.