The reproductive-age HIV prevalence in Swaziland was estimated to be 26% in 2007 (Central Statistical Office & Macro International, 2008). As there are no rigorous estimates of HIV prevalence for KP in Swaziland, the national prevalence was used as the base for sample size calculations in the current study. With this base rate in mind, we estimated that we needed 324 participants in each population group (MSM and FSW) in order to detect significant differences (odds ratio [OR] of 2.0) in HIV prevalence between participants with higher HIV-related protective behaviors (such as consistent condom use) and those with lower HIV-related protective behaviors with 95% confidence, 80% power, and a design effect of 1.5. This sample size allowed us to determine whether or not there were significant differences between these two groups per level of key social factors, such as experiences with stigma and discrimination.