The AIDS epidemic has created an unprecedented number of orphans. While largely absorbed by extended family, this additional responsibility can weigh heavily on their caregivers. The concept of caregiver burden captures multiple dimensions of well-being (e.g., physical, social and psychological). Measuring the extent and determinants of caregiving burden can inform the design of programmes to ease the negative consequences of caregiving. This study uses the baseline data from a study assessing interventions for orphans and vulnerable adolescents in the Eastern Cape, South Africa. Orphan caregivers (n = 726) completed an adapted version of the 12-item Zarit Burden Interview. In addition to basic caregiver and household demographics, the survey also collected information on AIDS-related illness and recent deaths. Descriptive data are presented, followed by multivariate Poisson regression models to explore factors associated with caregiver burden. Approximately 40% of caregivers reported high levels of orphan caregiving burden. Feelings of stress and inadequacy concerning their care responsibilities as well as anger towards the child were common. Household food insecurity was the most important predictor of orphan caregiving burden (marginal effect = 7.82; p < 0.001 for those reporting severe hunger); income was also a significant determinant. When other AIDS impacts were added to the model, only the AIDS-related illness of the caregiver was significantly associated with burden (marginal effect = 3.77; p < 0.001). This study suggests that caregivers with economic vulnerability and those struggling with their own AIDS-related illness feel most overburdened. These findings are particularly relevant to service providers who must identify caregivers in need of immediate assistance and allocate limited resources effectively. To alleviate caregiver burden, programmes must foster greater economic security (e.g., by facilitating access to social grants or directly providing cash transfers) and coordinate services with home-based care programmes serving the chronically ill.