Assimilation and acculturation have long been recognized as important though complex correlates of change in health risk profiles of immigrants and the resulting ethnic populations(1,2). The standard model that dominates research on acrulruration and health suggests that new immigrant populations typicdlly have a set of risk profiles that are distinctive from those of the population of the host society in which they have settled. These differences may reflect a combination of influences, including the maintenance of culturally distinctive behaviours characteristic of the country of origin; the distinctive influences of the immigration experience itself, including disruption of personal networks and exposure to discrimination; and the correlation of the decision to migrate across national boundaries with distinctive personal characteristics. Time spent in the host society — measured in years, and sometimes generations, among the descendents of immigrants — tends to erode these differences. Social epidemiologists frequently turn to the variables of time and, where relevant, linguistic change — the adoption of the language of the destination society — as correlates of changes in social and behavioural risk profiles away from those characteristic of the immigrant group itself, and towards those characteristic of segments of the broader population of the country of destination(1,3–5). Recently, increased anention has been given in the social epidemiology literature to the influence of the social-spatial context of health. In particular, a growing literature investigates variation in local social environments with respect to variables such as quality of food supply, local modelling of healthy diets and personal habits, stressfulness of daily living and encouragement of physical activity(6-10). In the context of the social scientific study of immigrant incorporation, this emphasis is concordant with a well-documented relationship linking ethnic residential enclaves with the maintenance and intergenerational transmission of ethnic-specific cultures(11-13). Drawing on these broader social science research findings, epidemiologists have investigated the hypothesis that ethnic concentration of immigrant-derived populations in neighbourhoods is associated with the maintenance of group-specific social behavioural practices that influence health outcomes. The Mexican-American population of the USA provides a particularly noteworthy case for the investigation of the effects of residential concentration on health. Compared with non-Hispanic whites, Mexican-Americans have lower mortality rates from all causes, and from leading causes including CVD and cancers at most common sites(13-18). Mexican-American mortality rates are consistently reported to be lower for immigrants than they are for Mexican-Americans born in the USA13,15,17-19). That mortality rates are lower for a Mexican-American population that is on average socia-economically disadvantaged has been described as an epidemiological paradox(20,21). One of the leading hypotheses about the better than expected health and mortality outcomes for Mexican-Americans, as well as the apparently poorer outcomes for US-born Mexican-Americans compared with immigrants from Mexico, points to protective aspecrs of health-related behaviours among immigrants, including healthier diets, lower rates of smoking, substance and alcohol use, and higher rates of physical activity(13,16,21,22). Indeed, studies of acculturation have documented a relationship between acculturation and less healthy lifestyles in the Mexican origin population, although effects of acculturation are not entirely negative. Notably, both health-care access and use of screening improves with greater acculturation. A small but growing number of studies have examined the hypothesis that a high concentration of Mexican populations in residential communities is associated with better health outcomes. To date, results have been mixed. Some studies report evidence of lower mortality, lower chronic disease morbidity, better mental health and higher self-rated health(23-31). Others report weak, contradicrory or null results(13,32,33). In the present study we investigate the relationship between ethnic residential concentration of Mexican-Americans and dietary intake. Specifically, we investigate the hypothesis that there is a strong relationship between ethnic concentration, e.g. residence in a barrio community, and types of foods consumed. This hypothesis has a high degree of plausibility, because a high level of ethnic concentration in a local community creates a context for the supply of ethnic-specific food products and for the modelling of dietary practices. The Mexican-American population lives in very diverse residential settings, ranging from homogeneous ethnic environments in near-border areas in the south-west, to neighbourhoods throughout the USA where they are highly integrated with no n-Hispanics. Do dietary practices among Mexican-Americans in different neighbourhood settings differ in ways that suggest that integration with other groups leads to deterioration of dietary practices that help explain the increaSing rates of chronic disease prevalence among more acculturated Hispanics?