PURPOSE. This study examines whether local income inequality is associated with an increased likelihood of obesity among Los Angeles County residents and whether collective efficacy mediates the relationship. DESIGN. A cross-sectional study of 2875 adults in 65 neighborhoods that took part in wave 1 of the Los Angeles Family and Neighborhood Survey in 2000-2001. Neighborhood measures are taken from the Los Angeles Neighborhood Services and Characteristics Database and decennial census. MEASURES. Obesity is defined as a body mass index over 30. Income inequality is operationalized with the Gini coefficient. Collective efficacy is a neighborhood-level measure comprised of aggregated responses to items that capture trust, cohesion, and the willingness to intervene for the common good among residents. Controls are included at the individual level for demographics and health characteristics, and at the neighborhood level for median household income. ANALYSIS. Logistic regression models of individuals within neighborhoods. RESULTS. When neighborhood economic well-being is controlled, income inequality is associated with a significant reduction in the likelihood of obesity while also controlling for individual demographic and health-related characteristics. Collective efficacy exerts an independent and beneficial effect but does not mediate the relationship between inequality and obesity. CONCLUSION. Neighborhood social resources and economic heterogeneity are associated with a lower likelihood of obesity. It may be that economically heterogeneous neighborhoods, perhaps especially in Los Angeles County, contain characteristics that promote health.