The study found that a neighborhood's degree of "collective efficacy"--defined as a close-knit neighborhood with residents who are willing to help each other--was linked to rates of preventable and health-related deaths only for children and adolescents under 18 years old. This supports the hypothesis that community residents focus their collective activities on protecting children from harm. An additional finding was that collective efficacy partially mediated the impact of economic disadvantage for neighborhood children. For both preventable and health-related deaths, the inclusion of collective efficacy in the model reduced the effect of economic disadvantage. These findings are consistent with previous research which has shown that increased levels of community social organization minimize community problems such as disorder, crime, poor health, and mortality. Further, communities that are organized for action have had greater success in the acquisition of government resources, including loans, increased police accountability, and the enforcement of housing and traffic codes. Data for this study were obtained from the 1995 Project on Human Development in Chicago Neighborhoods Community Survey. This project involved a probability sample of 8,782 Chicago residents who assessed the features of the communities where they lived. Mortality data were obtained from the Chicago Department of Public Health Epidemiology Program. Dependent variables were neighborhood rates of mortality between 1996 and 1998, rates of preventable youth deaths, rates of preventable adult deaths, and nonpreventable mortality rates. Independent variables were collective efficacy, prior mortality rates, economic disadvantage, residential stability, immigrant concentration, and population density. 3 tables, 4 notes, and 52 references