OBJECTIVES: Little is known about the impact of HIV infection on biological ageing in sub-Saharan Africa. The study aimed to assess biological ageing in South African HIV-infected adults and HIV-seronegative individuals using two validated biomarkers, telomere length and CDKN2A expression (a mediator of cellular senescence). DESIGN: A case-control study. METHODS: Two hundred and thirty-six HIV-infected adults aged at least 30 years and 250 age and sex frequency matched HIV-seronegative individuals were recruited from clinics in township communities in Cape Town. Biological ageing was evaluated by measurement of telomere length and CDKN2A expression in peripheral blood leukocytes. RESULTS: The median ages of the HIV-infected and HIV-seronegative participants were 39 and 40 years, respectively. Among HIV-infected participants, 87.1% were receiving antiretroviral therapy (ART), their median CD4⁺ cell count was 468 cells/μl and 84.3% had undetectable viral load. Both biomarkers were validated against chronological age in HIV-seronegative individuals. Telomere length was significantly shorter in HIV-infected individuals than in HIV-seronegative individuals (mean relative T/S ratio ±SE:0.91 ± 0.007 vs. 1.07 ± 0.008, P < 0.0001). CD2NKA expression was higher in HIV-infected participants than in HIV-seronegative individuals (mean expression: 0.45 ± 0.02 vs. 0.36 ± 0.03, P = 0.003). Socioeconomic factors were not associated with biological ageing in HIV-infected participants. However, in participants on ART with undetectable viral load, biomarker levels indicated greater biological ageing in those with lower current CD4⁺ cell counts. CONCLUSION: Telomere length and CDKN2A expression were both consistent with increased biological ageing in HIV-infected individuals. Prospective studies of the impact of HIV on biological ageing in sub-Saharan Africa are warranted.