A growing body of research demonstrates that having multiple adverse biological risk factors – such as hypertension, obesity, high blood sugar, and elevated cholesterol – increases the risk of morbidity, functional and cognitive decline, and mortality (1-16). Such research also suggests that racial/ethnic minority groups and people with lower levels of education and income tend to accumulate more biological risk factors (4, 6, 9, 10, 17-20), making the cumulative toll of such “wear and tear” to the body a potentially critical, though not yet widely recognized, facet of health disparities in the United States. In an influential essay on the pathways from stress to disease, McEwen and Stellar (21) coined the term allostatic load to describe the harmful effects of physiological response patterns that can ensue from prolonged exposure to stressful environments or being highly reactive to stressors. They described a process in which the body responds to physical, psychosocial, and environmental stressors by producing hormones and neurotransmitters that help the body respond to stress by coordinating physiological responses across multiple biological systems, thus achieving stability through change (22). In the face of severe or prolonged stress, dysfunctions can result from physiological systems being activated too frequently, not having a chance to return to their setpoints, or ceasing to activate adequately. Moreover, dysfunctions of one physiological system can spillover into related systems. For example, exposure to stress can trigger surges in blood pressure, which in turn can accelerate atherosclerosis or interact with metabolic processes to produce Type II diabetes (22). Thus, the theory of allostatic load offers a framework for understanding not only the pathways between stress and disease but also how physiological pathologies can spread across systems and cumulatively affect health. There is a growing literature on how to measure allostatic load in population-based research. Most studies of this kind create indices of allostatic load from biomarkers of metabolic, inflammatory, cardiovascular, and neuroendocrine processes. There is substantial variation across studies in how many biomarkers are included in such indices, which physiological systems are represented, and how the indices are formulated [for a comprehensive review, see Juster, McEwen, and Lupien (23)]. In this study we follow an approach similar to prior studies but use the term “cumulative biological risk” (CBR) rather than allostatic load to describe indices of this kind to acknowledge that they are indirect indicators (at best) of the underlying processes that generate allostatic load. That is, like other studies, we do not have measures of primary stress mediators and instead have secondary outcomes that reflect adaptive physiological responses to stress and other adverse stimuli but which also can arise from other etiologies. Although some scholars use the term “allostatic load” in reference to similar measures, we did not want to give readers the impression that we were directly operationalizing the concept of allostatic load and thus preferred the term CBR. It is worth noting that metabolic syndrome describes a cluster of risk factors that overlaps considerably with those in our measure of CBR, although conceptually allostatic load addresses a broader array of systems in dysregulation. Both of these concepts describe a potentially interrelated set of physiological conditions that may have cumulative and interactive effects on health. Several studies show that racial/ethnic minorities and/or people of lower social status experience a greater accumulation of biological risk factors (11, 24). For example, in an analysis of the Normative Aging Study (24), Kubzansky and colleagues found that respondents with lower levels of education experienced higher levels of cumulative biological risk. In Weinstein and colleagues’ study using both the MacArthur Study of Successful Aging and Taiwan Social Environment and Biomarkers of Aging Study (SEBAS) cohorts (25), income and education were inversely related to CBR. Likewise, higher levels of education and income were associated with lower CBR in Seeman and colleagues’ (26) analysis of the National Health and Nutrition Examination Study (NHANES III). Respondents with a poverty-income ratio less than 1.85 were more likely than the non-poor to have high CBR in Geronimus and colleagues’ analysis of NHANES III, and they also found racial differences in CBR, with higher risks for respondents in the non-poor black category compared to poor whites (6). Several other studies have also shown that blacks (6, 9, 19, 26) and Hispanics (9, 19) have significantly more risks than whites, independent of education and income. Neighborhood environments are often invoked as a possible explanation for social disparities in health. In their study of NHANES III, Bird and colleagues (27) found that neighborhood socioeconomic status was associated with a higher count of biological risks after adjustment for age, gender, race/ethnicity, marital status, nativity, education, and an income to poverty ratio. Merkin and colleagues (28) expanded on the analysis by Bird and colleagues, using models stratified by race/ethnicity to show that the relationship between neighborhood disadvantage and CBR is strongest among blacks and, to a lesser extent, Mexican Americans. Neither study assessed the degree to which neighborhood factors explain racial/ethnic differences in CBR; Merkin and colleagues cite insufficient overlap in the distribution of neighborhood disadvantage between blacks and whites as an obstacle to such an analysis using the NHANES data (28). Thus, to date, no study has provided a systematic account of how much individual-level disparities are a function of or conditioned by neighborhood context (29). This paper (1) assesses the contribution of neighborhood environments to racial/ethnic and socioeconomic disparities in CBR, using data from a population-based study of adults in Chicago, and (2) shows that the relationship between neighborhood socioeconomic position and CBR may be driven less by the factors that indicate neighborhood disadvantage (e.g., aggregate income levels and rates of poverty, unemployment, public assistance) and more by factors that may be more indicative of relative neighborhood affluence (e.g., aggregate education levels, occupational composition, and home values).