In South Africa, up to 40% of pregnant women are living with human immunodeficiency virus (HIV), and 30â45% are obese. However, little is known about the dual burden of HIV and obesity in the postpartum period. In a cohort of HIVâuninfected and HIVâinfected pregnant women initiating antiretroviral therapy in Cape Town, South Africa, we examined maternal anthropometry (weight and body mass index [BMI]) from 6 weeks through 12 months postpartum. Using multinomial logistic regression, we estimated associations between baseline sociodemographic, clinical, behavioural, and HIV factors and being overweightâobese I (BMI 25 to <35), or obese IIâIII (BMI >35), compared with being underweight or normal weight (BMI <25), at 12 months postpartum. Among 877 women, we estimated that 43% of HIVâinfected women and 51% of HIVâuninfected women were obese IâIII at enrollment into antenatal care, and 51% of women were obese IâIII by 12 months postpartum. On average, both HIVâinfected and HIVâuninfected women gained, rather than lost, weight between 6 weeks and 12 months postpartum, but HIVâuninfected women gained more weight (3.3 kg vs. 1.7 kg). Women who were obese IâIII preâpregnancy were more likely to gain weight postpartum. In multivariable analyses, HIVâinfection status, being married/cohabitating, higher gravidity, and high blood pressure were independently associated with being obese IIâIII at 12 months postpartum. Obesity during pregnancy is a growing public health concern in lowâ and middleâincome countries, including South Africa. Additional research to understand how obesity and HIV infection affect maternal and child health outcomes is urgently needed.