A cross sectional survey was administered to 670 men who have sex with men (MSM) and transgender women (TW) in San Salvador through respondent driven sampling to identify determinants of ever testing for HIV using a minority stress framework. A positive association was found between ever testing and older age [adjusted odds ratio (aOR) 2.10], past experience of sexual assault (aOR 2.92), perceiving that most social acquaintances had tested (aOR 1.81), and knowing a PLHIV (aOR 1.94). A negative association was found between homelessness and ever testing (aOR 0.43). Among the MSM sub-sample (n = 506), similar results were found for older age (aOR 2.63), and past experience of sexual assault (aOR 2.56). Internalized homonegativity was negatively associated with ever testing for HIV among MSM (aOR 0.46), and HIV testing stigma and experienced provider discrimination further strengthened this relationship. It is important to mitigate sexual minority stigma in order to increase HIV testing among MSM. Future research should explore this construct among TW.