Asthma morbidity and mortality are not distributed homogeneously among populations. To assess the relationship between asthma hospitalization rates and socioeconomic factors, we conducted an ecologic analysis using small geographical areas defined by postal zip code in New York City. Asthma hospitalization rates correlated with low median family income, percentage of minorities in the population, and percentage of children under the age of 18. Lack of access to preventive health care, poor housing conditions, environmental exposures, and genetic susceptibility may contribute to high incidence of asthma in some neighborhoods. This report supports the role of socioeconomic factors in asthma and serves to provide data for regulatory and health agencies to concentrate their efforts on neighborhoods most in need.