One quarter of pregnant women in Zambia are infected with HIV. Understanding how knowledge of HIV relates to personal risk perception and avoidance of risky behaviors is critical to devising effective HIV prevention strategies. In conjunction with a large clinical trial in Lusaka, Zambia, we surveyed postpartum women who had been tested for HIV but did not know their status before undergoing the questionnaire. Of 858 women for whom complete data were available, 248 (29%) were HIV infected. Women 22 years of age or older (adjusted odds ratio [AOR], 1.7; 95% confidence interval [CI], 1.1-2.5), women reporting > or =2 sexual partners in their lifetime (AOR, 1.8; 95% CI, 1.3-2.5), and women reporting a history of a sexually transmitted infection (AOR, 2.7; 95% CI, 1.7-4.3) were more likely to be HIV infected. Having had > or =2 lifetime sexual partners was a marker for perception of high personnel risk for HIV infection (AOR, 1.5; 95% CI, 1.1-2.1). However, there was no relationship between perceived risk of HIV infection and actual HIV status. In fact, 127 (52%) of 245 women who stated that they were at no or low risk for HIV infection were HIV infected. Living in an area of high HIV seroprevalence like Zambia seems to be the greatest risk factor for infection in unselected pregnant women. Before significant inroads can be made in decreasing the incidence of HIV infection among pregnant women, population-based strategies that involve men must be implemented.