The goal of this study was to improve understanding of whether incorrect HIV/AIDS heuristics and characteristics-based risk theories are barriers to HIV prevention among young African-Americans at increased risk for HIV. We explored: (1) the beliefs of men and women regarding disease prevention strategies, and (2) the relationship of such beliefs to safer sexual behaviours. In Phase I, semistructured individual interviews were conducted with both members of 22 heterosexual couples at increased risk for HIV/STIs. Subsequently, in Phase II, structured individual interviews were conducted with another 40 women and 40 men (not couples). Participants in Phase I reported use of condoms and monogamy as major strategies for disease prevention. The beliefs that were endorsed by the largest percentage of Phase II participants were related to the 'known partners are safe partners' and 'trusted partners are safe partners' heuristics. Moreover, stronger endorsement of the 'known partners' heuristic was negatively associated with measures of condom use and pregnancy prevention behaviour. Our findings highlight the need for interventions and programmes to encourage intimate partners to consistently use condoms until both members of the dyad are tested and agree to mutual monogamy.