BACKGROUND: Accurately identifying individuals who are on antiretroviral therapy (ART) is important to determine ART coverage and proportion on ART who are virally suppressed. ART is also included in recent infection testing algorithms used to estimate incidence. We compared estimates of ART coverage, viral load suppression rates and HIV incidence using ART self-report and detection of antiretroviral (ARV) drugs and we identified factors associated with discordance between the methods. METHODS: Cross-sectional population-based survey in KwaZulu-Natal, South Africa. Individuals 15-59 years were eligible. Interviews included questions about ARV use. Rapid HIV testing was performed at the participants' home. Blood specimens were collected for ARV detection, LAg-Avidity HIV incidence testing and viral load quantification in HIV-positive individuals. Multivariate logistic regression models were used to identify socio-demographic covariates associated with discordance between self-reported ART and ARV detection. RESULTS: Of the 5649 individuals surveyed, 1423 were HIV-positive. Median age was 34 years and 76.3% were women. ART coverage was estimated at 51.4% (95%CI:48.5-54.3), 53.1% (95%CI:50.2-55.9) and 56.1% (95%CI:53.5-58.8) using self-reported ART, ARV detection and both methods combined (classified as ART exposed if ARV detected and/or ART reported) respectively. ART coverage estimates using the 3 methods were fairly similar within sex and age categories except in individuals aged 15-19 years: 33.3% (95%CI:23.3-45.2), 33.8% (95%CI:23.9-45.4%) and 44.3% (95%CI:39.3-46.7) using self-reported ART, ARV detection and both methods combined. Viral suppression below 1000cp/mL in individuals on ART was estimated at 89.8% (95%CI:87.3-91.9), 93.1% (95%CI:91.0-94.8) and 88.7% (95%CI:86.2-90.7) using self-reported ART, ARV detection and both methods combined respectively. HIV incidence was estimated at 1.4 (95%CI:0.8-2.0) new cases/100 person-years when employing no measure of ARV use, 1.1/100PY (95%CI:0.6-1.7) using self-reported ART, and 1.2/100PY (95%CI:0.7-1.7) using ARV detection. In multivariate analyses, individuals aged 15-19 years had a higher risk of discordance on measures of ARV exposure (aOR:9.4; 95%CI:3.9-22.8), while migrants had a lower risk (aOR:0.3; 95%CI:0.1-0.6). CONCLUSIONS: In KwaZulu-Natal, the method of identifying ARV use had little impact on estimates of ART coverage, viral suppression rate and HIV incidence. However, discordant results were more common in younger individuals. This may skew estimates of ART coverage and viral suppression, particularly in adolescent surveys.