HIV stigma - both 'self-stigma' towards positive individuals and 'stigma by association' towards their families - is linked with adverse mental health. This study examined how stigma was associated with the mental health of parents and children in South Africa. Parent-child dyads (n=2477 dyads) in South Africa participated in a cross-sectional survey. For both parents and children, greater stigma was associated with their own reports of greater anxious and depressive symptoms. Parents reports of stigma was associated with children's greater anxious and depressive symptoms. Children's reports of stigma was related to parents greater anxious and depressive symptoms. There was a significant interaction, such that the association between parent stigma and depression was stronger when children also reported high levels of stigma. Findings provide support the effect of HIV stigma on the mental health of families and illustrate the importance of taking a family-based approach to stigma-reduction interventions to alleviate mental health problems.