Drawing on long-term ethnographic fieldwork on older caregivers and their shifting roles since the introduction of antiretroviral therapy in northwest Tanzania, this article explores grandmothers’ roles in caring for grandchildren who are HIV positive and on treatment. While AIDS treatment programmes usually focus on cultivating expert patients who can perform self-care, this study focuses on older caregivers and how they become experts in caring for their grandchildren living with HIV. How is expert care enacted and what supports or limits its quality? Based on observations and in-depth interviews, this article argues that grandmothers become ‘expert caregivers’ by merging knowledge acquired in the clinic and support groups with intimate practices of grandparental care. However, the grandmother’s gendered and generational position within kin networks affects her ability to provide expert care. The findings indicate that in analysing treatment outcomes among adolescents, it is important to understand the broader family dynamic that influences the actual possibility of expert caregivers to support children living with HIV.