Cognitive barriers to participation in actual HIV vaccine trials have not been previously comprehensively reviewed. In this review article, barriers in actual early phase, phase 2B, and phase 3 HIV vaccine trials are quantified and categorized, and compared between the Organization for Economic Co-operation and Development (OECD) countries and the non-OECD countries. Participation rates were standardized to allow for comparisons. In both the OECD and the non-OECD countries, barriers included subjective norms and discrimination, vaccine safety concerns, and logistical concerns. More actual HIV vaccine trials can incorporate questions about and quantify barriers to participation, and this may aid future recruitment strategies.