Since 1996, demand for emergency services in the United States has been rising (1). While the number of emergency departments (EDs) across the country has decreased, the number of ED visits has increased (1). As a result, EDs are experiencing higher patient volume and overcrowding, and patients seeking care are experiencing longer wait times (2,3). As national health care costs continue to rise and policymakers become increasingly interested in ways to make the health care system more efficient, it is important to understand the characteristics of those individuals who use EDs--often in place of other sources of ambulatory care.