Background: Prevention of unplanned pregnancy is a crucial aspect of preventing mother-to-child HIV transmission (PMTCT). However, we have little understanding of how HIV status and antiretroviral therapy (ART) may influence pregnancy planning. There are few data on pregnancy planning in HIV-infected South African women, and no comparative data with HIV-uninfected women. Methods: We conducted a cross-sectional study of 2105 pregnant women (1512 HIV-infected; 593 HIV-uninfected) ages 18-44 making their first antenatal clinic visit at a primary-level health care facility in Gugulethu, Cape Town. All women completed structured questionnaires including the London Measure of Unplanned Pregnancy (LMUP), a 6-item scale that categorizes pregnancies into planned, ambivalent and unplanned. Analyses examined LMUP results across 4 groups of participants: HIV-infected established on ART; known HIV-infected but not currently on ART; newly diagnosed HIV-infected; and HIV-uninfected. Results: Overall, the mean age was 29 years (SD: 5.63), 43% of women were married or cohabiting and 20% were nulliparous. The LMUP performed well across all groups (Cronbach's α=0.84). Levels of unplanned pregnancy were higher in HIV-infected versus HIV-uninfected women (50% vs. 33%, p<0.001); and highest in women not on ART. Overall, 69% of women reported contraceptive use in the year before pregnancy; this was strongly associated with unplanned pregnancy (p<0.001). Compared to HIV-uninfected women, HIV-infected women had significantly higher odds of unplanned pregnancy, even after adjusting for age, parity and cohabiting status. The odds were greatest among women newly-diagnosed with HIV and previously diagnosed but not on ART (OR: 1.43; 95% CI: 1.05-1.94 and OR: 1.56; 95% CI: 1.13-2.15, respectively). Increased parity and age <24 years were also associated with unplanned pregnancy (OR 1.83; 95% CI: 1.24-2.74 and OR 1.42; 95% CI: 1.25- 1.60 respectively). Conclusions: These data indicate high levels of unplanned pregnancy in a high HIV prevalence setting, highlighting missed opportunities for family planning and counselling services for HIVpositive women. Possible explanations for the high level of unplanned pregnancy observed include contraceptive failure and/or misuse thereof. Therefore, women living with HIV require additional support to avoid unplanned, particularly those who are younger and have one or more children.