Background: In 2019, about 1.7 million adolescents between the ages of 10 and 19 years were living with HIV worldwide, of which 170 000 were newly infected with HIV in 2019. South Africa has the highest number of persons living with HIV. Although there has been major improvement in access to antiretroviral therapy (ART), it is still unclear what proportion of adolescents (aged 10–19 years) are virally suppressed in the provinces of South Africa.Objectives: To determine the prevalence of and the factors associated with viral suppression among adolescents (10–19 years) on ART in the Thabo Mofutsanyane District Municipality of the Free State province of South Africa.Method: A retrospective cross-sectional analysis of demographic, clinical and treatment-related information that were extracted from an electronic database was conducted using Statistical Package for the Social Sciences version 26.Results: The median duration on ART was 6.58 years. Although 78% (n = 4520) of adolescents living with HIV who were on ART achieved viral suppression ( 1000 copies/mL), only 9.5% (n = 430) were fully suppressed at 50 copies/mL. In multivariate analysis, the odds of being virally suppressed reduced with increasing age at ART initiation. Adolescents with CD4 counts greater than 500 cells/mm3 at baseline had a higher odds ratio of viral suppression (adjusted odds ratio [AOR]: 1.77; confidence interval [CI]: 1.28–2.47). The odds of viral suppression were significantly lower among those not retained in care (AOR: 0.45; CI: 0.35–0.58).Conclusion: Tailored interventions should be developed to improve viral suppression among adolescents on ART.