Injection drug users (IDUs) are a difficult population study due to the unique social and environmental factors that affect their risk of disease infection and health outcomes. Studies have shown that injection drug users are highly mobile, which is a behavior that could put them at an increased risk for transmission of blood-borne infections and in particular, HIV. However, there is a disparity between the actual risk of transmission and the perceived risk indicating that although IDUs may be more susceptible to being infected with HIV, they may not perceive that they are more susceptible to infection. To date, there are no studies that specifically examine the effects of travel to and injection of illicit drugs in Mexico to perception of risk in the San Diego-Tijuana border region. Furthermore, studies that have been done on risk perception and mobility in other locations are not readily applicable to this population. This investigation attempts to analyze how the risk factors, travel to and injection of illicit drugs in Mexico, affect one's perceived susceptibility to HIV. This health outcome was selected on the basis of the Health Belief Model, which suggests that those who perceive a risk to a disease or condition will be more likely to change risky behaviors, thereby preventing their infection and transmission of that disease. Data from this analysis was gathered from the Study to Assess Hepatitis C Risk (STAHR), which was conducted from March 2009 to June 2010 under the Division of Global Public Health at the University of California, San Diego. Five hundred and sixty-six injection drug users aged 18-40 years old were recruited to participate in this study which also examined socio-demographic variables, injection and sexual factors that could influence behavior. Findings from this study suggest that travel and injection of illicit drugs in Mexico does not result in an increased perception of HIV risk however further studies should be performed on this topic that also incorporate social and environmental factors.