ABSTRACT: Hotspots: Understanding Areas of Concentrated Alcohol and Drug Problems at the US- Mexico Border Millions of Mexican Americans live in the US-Mexico border region, which is both an extremely disadvantaged area and a staging zone for migration to the interior. Thus, the health and substance use patterns of Mexican- origin border residents are of central concern. Nevertheless, despite preliminary evidence of high drug trafficking, drug availability, and substance use problems along the border, very little is known about alcohol and drug problems in this area. Our team recently initiated a large epidemiological study, the US-Mexico Study of Alcohol and Related Conditions, or UMSARC (R01AA018365; PI's Cherpitel and Borges), to address this gap. In addition to being one of only two large-scale epidemiological studies of the border addressing alcohol, UMSARC is the only known such study to survey residents of both the US and Mexico. Data represent 4,796 in-person interviews with a probability sample of Mexican and Mexican-origin individuals interviewed between 2011-2013. Emerging papers based on UMSARC data suggest a heightened risk for alcohol and drug problems, yet substantially lower substance use treatment utilization, at the US border, compared to the interior. Yet, preliminary evidence also suggests dramatic, unexplained variation even among border sites, with alcohol and drug problems being concentrated in a single US hotspot: Laredo, Texas. Preliminary, unpublished analyses also point to Nuevo Laredo, Laredo's sister city, as a hotspot for drug problems. This suggests that the local environment may play a critical role in alcohol and drug outcomes at the border—and perhaps among Latinos generally. A deeper understanding of the role of environmental factors in this apparent concentration of problems in border hotspots would help shed light on core processes in the epidemiology of substance abuse as well as possible points of intervention relevant to Latinos in the border region and more broadly. However, additional research is needed to 1) better characterize and contextualize variation across UMSARC sites in alcohol- and drug-related outcomes; 2) delineate the roles of specific environmental (and other) factors in explaining this variation; and 3) better understand pathways of influence between the US and Mexico, and how US-Mexico interactions may contribute to elevations of problems. The current project proposes to address these gaps. Aim 1 will better characterize the distribution of alcohol use and problems, drug use and problems, and substance use treatment utilization across study sites and relative to regional and national estimates. Aims 2 and 3 will involve geocoding the data to test roles for key neighborhood variables in explaining geographic variation in alcohol- and drug- related outcomes. Aim 4 will directly explore potential pathways of influence between Mexico and the US using existing and geocoded variables. Analyses will leverage a uniquely rich and well-powered dataset to extend the very limited knowledge base on alcohol and drug use and problems at the border, as well as improve understanding of environmental influences on these outcomes among Latino populations.