The stigma related to HIV/AIDS poses a challenge to the lives of people living with HIV/AIDS (PLWHA). These are worsened when people who are important in the lives of PLWHA manifest it, such as health professionals. This is particularly true for physicians who represent the first line of contact for treatment and the basis of knowledge of effective strategies to treat the disease. When physicians stigmatize PLWHA access to effective treatment can be hindered. Previous studies carried out by the research team in Puerto Rico show that health professionals, particularly physicians, manifest high levels of HIV/AIDS stigma. Scientifically tested strategies to reduce such stigma are urgently needed and should be provided during their professional training since they are open to learning new ideas about the physician’s role in the lives of people who are ill. Still, a review of the published literature on HIV/AIDS stigma reduction evidences a lack of scientifically tested interventions targeting medical students. This five-year R01 study aims to revise and test the efficacy of an intervention to reduce HIV/AIDS stigma among medical students through a randomized control trial. The specific aims of the proposed research are: Aim 1: Revise and implement an intervention based on Social Cognitive Theory to reduce HIV/AIDS stigma and evaluate its acceptability among medical students in their last year of training. Aim 2: Evaluate the intervention’s efficacy in reducing HIV/AIDS stigma attitudes and behaviors immediately after the intervention, at six months, and 12 months time. Aim 3: Evaluate whether proposed mechanisms of stigma change, specifically HIV information, skills for identifying stigma and interacting with PLWHA, and self-efficacy for such skills, explain stigma reduction after the intervention. These aims will be carried out though a randomized control trial implemented in two stages. In Stage 1, we will revise an existing intervention to reduce HIV/AIDS stigma among health professionals based on our previous research. This pilot intervention has been tested and shows promising results in reducing HIV/AIDS stigma with statistically significant reductions in our stigma measurements. In stage two, the intervention will be implemented among a sample of 500 medical students who will be randomly assigned to intervention (n=250) and control groups (n=250) and subjected to a process and impact evaluation administering a quantitative questionnaire before, immediately after, at six months, and 12 months after the intervention. This study will entail the first HIV/AIDS stigma reduction intervention targeting medical students in Puerto Rico that will be experimentally tested with random samples and long term assessment of change. Reducing HIV/AIDS stigma among this population can foster the provision of stigma free services and provide a framework for future interventions. This study will entail the first HIV/AIDS stigma reduction intervention targeting Latino medical students that will be experimentally tested with random samples and long term assessment of change, as we have been unable to find others in the published scientific literature. If proven effective it will be disseminated and will contribute to AIDS stigma reduction among several medical training programs in Puerto Rico, and other applicable Spanish speaking scenarios. Reducing HIV/AIDS stigma among this population can foster the provision of stigma free services which research has shown to better the lives of people with HIV/AIDS.