Marriage presents the single greatest risk for HIV infection among women in rural Mexico. We drew on 6 months of participant observation, 20 marital case studies, 37 key informant interviews, and archival research to explore the factors that shape HIV risk among married women in one of the country's rural communities. We found that culturally constructed notions of reputation in this community lead to sexual behavior designed to minimize men's social risk (threats to one's social status or relationships), rather than viral risk and that men's desire for companionate intimacy may actually increase women's risk for HIV infection. We also describe the intertwining of reputation-based sexual identities with structurally patterned sexual geographies (i.e. the social spaces that shape sexual behavior). We propose that, because of the structural nature of men's extramarital sexual behavior, intervention development should concentrate on sexual geographies and risky spaces rather than risky behaviors or identities.