Background: Progress has been made to increase access to antiretroviral therapy (ART) for adolescents living with HIV (ALHIV) to improve their survival, but ALHIV still have worse treatment adherence and viral suppression compared to adults and children.Objective: To determine the prevalence of viral suppression and the associated factors among adolescents aged 10–19 years on ART at an urban public primary healthcare facility in the Sedibeng district, Gauteng.Method: A cross-sectional survey was conducted among 192 adolescents who were on ART for at least six months between 2015 and 2018. A self-developed data extraction tool was used to collect data from the Tier.Net electronic database and clinical folders. Data were captured on Microsoft Excel, and descriptive and inferential analyses were performed using SPSS 27 statistical software.Results: The median age at ART initiation of adolescents was 9.0 years (interquartile range [IQR]: 5.0–12.0), and the median duration on ART was 70.5 (IQR: 30.25–105.5) months. The prevalence of viral suppression ( 1000 copies/mL) among adolescents on ART was 74%, with 41% achieving full suppression ( 50 copies/mL). Those adolescents who reported optimal ART adherence were more likely to be virally suppressed compared to those who reported poor adherence (98.1% vs 25.0%; p ≤ 0.001).Conclusion: Adolescent viral suppression of 74% is higher than in comparable sites, but still way too short of the UNAIDS target of 90%. We recommend adherence support for adolescents to achieve viral suppression.Contribution: The study highlights the urgent need for targeted adherence support interventions for adolescents living with HIV on antiretroviral therapy to improve rates of viral suppression to meet UNAIDS target of 95%.