Increasing availability of antiretroviral treatment (ART) has led HIV to be considered a chronic disease, shifting attention to focus on quality of life including mental wellbeing. We investigated knowledge and causal attributions for mental disorders in HIV-positive children and adolescents in rural and urban Uganda. This qualitative study was nested in an epidemiological mental health study among HIV-positive children and adolescents aged 5-17 years in rural and urban Uganda. In-depth interviews were conducted with caregivers of HIV-positive children (5-11 years) and adolescents (12-17 years) in HIV care. Interviews were audio recorded with permission from participants and written consent and assent sought before study procedures. Thirty eight participants (19 caregivers, 19 children/adolescents) were interviewed. Age range of caregivers was 28-69 years; majority were female (17). Caregivers had little knowledge on mental disorders ;only 3 related the vignette to a mental problem  and attributed it to: improper upbringing, violence, poverty and bereavement. Five adolescents identified vignettes as portraying mental disorders caused by: ill-health of parents, bereavement, child abuse, discrimination, HIV and poverty. Caregivers are not knowledgeable about behavioural and emotional challenges in HIV-positive children/adolescents. Mental health literacy programmes at HIV care clinics are essential to enhance treatment-seeking for mental health.