The influx of Latino laborers into the U.S. and the confluence of migration-driven factors in an environment ripe for risk-taking have the potential to exacerbate already rising STI/HIV rates among migrants and their social networks at both the home and receiving regions. This paper focuses on Mexican migrant laborers who are among the most marginalized and exploited Latinos in the U.S. This study used ethnographic methods to delineate the sociocultural and spatial contexts and social organization of migrant farmwork, and examined how intertwined individual and environmental factors render migrant farmworkers vulnerable to STI/HIV risks. Findings indicate the presence of a number of factors in the study population of Mexican migrant workers (N = 23)-such as poverty, limited education, physical/social/cultural isolation, long work hours, constant mobility, hazardous work conditions, limited access to health care, low rates of condom use, multipartnering, and use of sexworkers-which increase their risks for STI/HIV transmission. To be successful, prevention efforts need to focus not only on condom education and HIV awareness and testing, but also on reducing migrants' social isolation and understanding their social networks.