Social networks expand rapidly in adolescence, increasing HIV status disclosure considerations and concerns for young people living with HIV, especially in settings where HIV-related stigma is prevalent. This study examines HIV disclosure and enacted stigma among adolescents and young adults living with HIV in South Africa. This study uses survey data from a sample of 1186 youth living with HIV, aged 14–24, and enrolled in peer support groups led by community-based organizations in KwaZulu Natal and Gauteng provinces, South Africa. Study participants completed a questionnaire on sociodemographic details, physical health, school attendance, who knew the individual’s HIV status, and experiences of HIV-related mistreatment. Mixed effects logistic regression examined the association between experiences of HIV-related mistreatment and factors that may inadvertently disclose one’s status, such as poor physical health and missed school, and knowledge of an individual’s HIV-positive status by their caregiver, household, friends, educators, and most recent sexual partner. Almost a quarter of the sample reported an experience of HIV-related mistreatment in the past six months. After controlling sociodemographic characteristics, missed school due to illness (AOR = 1.75, 95% CI = 1.27–2.43), and knowledge of HIV status by non-family members (AOR = 2.19, 95% CI = 1.60-3.00) were significantly associated with HIV-related mistreatment. Findings suggest that experiences of enacted stigma are common among youth and linked to poor physical health and knowledge of HIV status outside the family. Effective community-level stigma reduction interventions are urgently needed. In the meantime, adolescents need individualized disclosure counseling and support managing their physical health to prevent further inadvertent disclosure and discrimination.