Mobile populations present particular challenges for the delivery of health services. This paper focuses on a highly mobile population-truck drivers who cross the Mexico-Guatemala border through Ciudad Hidalgo in Chiapas-and examines the impact of an intervention that provided information regarding STD/HIV/AIDS, and promoted condom use. Following an ethnographic study to identify key actors, interaction sites and sexual practices, a baseline questionnaire survey was administered to 307 truck drivers. Information gathered in both the ethnographic study and the survey was used to design a series of interventions to promote condom use and provide information about STD/HIV transmission. Perceptions of risk for HIV/AIDS were lower for truck drivers in the intervention group compared with the baseline survey, an effect associated with greater reported condom use by truck drivers in this group. Border crossings are strategic setting for prevention interventions regarding STD/HIV/AIDS. Strategies must be developed to capitalize upon this as part of broader health promotion efforts. Inglés