OBJECTIVES Emergency departments (ED) are designed to provide unexpected care for seriously ill and injured persons, but people may seek care in EDs for other reasons as well. In 2005, for example, 13.9% of ED visits in the United States were considered non-urgent. Non-emergency use of the ED contributes to increased health care costs and may indicate that access to health care is limited. The purpose of this project was to describe and elicit determinants of ED use in a sample of economically disadvantaged persons METHODS We searched the published, English-language biomedical literature for articles on costs, cost-sharing, and ED use, for all years included in Medline, 1950 to the present. RESULTS In 2005, of 115.3 million ED visits, 13.9% were considered non-urgent (requiring attention within 2-24 hours). In an analysis of data from 2000 – 2001, Hunt et al found that frequent (>4/year) ED use was positively associated with poor physical and mental health. Hsu et al reported that ED copays in insured persons from $1 to $100 were associated with lower ED use, but not with poor outcomes. Wharam et al found that, from 2001 - 2005, higher-deductible insurance was associated with decreased ED visits among persons with employer-based health insurance, but not with a decrease in the odds for a first ED visit. CONCLUSIONS Programs to decrease ED use, such as cost-sharing, have been evaluated, but studies to evaluate these types of policies have typically focused on insured individuals. As a result, there is an important gap in understanding the epidemiology and economics of ED use among low-income, uninsured, and underinsured persons.