There has been significant debate, specifically within the African context, regarding the validity of using HCT data as part of routine surveillance data for the HIV epidemic. The use of HCT data in tracking the prevalence of HIV, as well as in estimating incidence rates for HIV, has been applied in some African countries, and may offer opportunities to strengthen surveillance in the Gauteng Province, South Africa. Literature suggests HCT data are biased as a result of the high proportion of repeat testers, where repeat testing may be related to high risk sexual behaviour. (1–8) It has been suggested that HCT data be separated into first-time- and repeat tester data in prevalence or incidence estimations. (9) The aim of this research was to determine if there are demographic and HIV prevalence differences between first-time- and repeat testers, as suggested in the literature. (9) Existing mobile HCT unit data was used from the Foundation for Professional Development (FPD). The data was collected in the Tshwane Metropolitan Municipality, Gauteng Province, South Africa. An observational, cross-sectional study design was applied. A systematic random sample of 400 first-time testers and 400 repeat-testers was drawn and analyzed. The findings of this study indicated an overall 10.0% (n=80) HIV prevalence rate. When compared to the Gauteng adult prevalence (15+) of 14.4%, the study prevalence is lower. (10) When looking at the characteristics of the first-time tester and repeat tester groups, there was an HIV prevalence rate of 12.5% (n=51/407, p=0.0152) in the first-time tester group, and 7.4% (n=29/393, p=0.0152) HIV prevalence rate in the repeat tester group. Although literature suggests that repeat testers are the more at risk population, the finding in this study clearly demonstrates that there is a difference in HIV prevalence between first-time- and repeat testers. When first-time/repeat tester was used as the dependent variable, it was found that females are 0.6 less times likely to be a first-time tester compared to males (OR=0.6, p=0.001). The finding of a difference in HIV prevalence between first-time- and repeat tester groups was consistent with three other studies in Ethiopia, Uganda and Kenya. In these studies, HIV prevalence in first-time testers was slightly higher than in that of repeat-testers. (3,11,12) It was found that there is a difference in the HIV and demographic profile between those who test for HIV for the first time and those who are repeat testers. The perceived risk and vulnerability to HIV plays a heavy role in motivating individuals to test once, or repeatedly. In regards to disease surveillance, this study did not prove that the population that utilises mobile HCT are representative of the Tshwane population. This study highlighted the need to better understand the sub-groups and characteristics of those who test for the first-time and those who test repeatedly for HIV. In conclusion, this study has provided evidence that there is a difference between the HIV prevalence of first-time- and repeat testers. However, there is good reason to doubt that the prevalence rate of first-time testers is genuine. Copyright / Dissertation (MSc)--University of Pretoria, 2013. / School of Health Systems and Public Health (SHSPH) / Unrestricted