In emergency medicine, there is an ongoing debate regarding patients who use the emergency department (ED) as their usual source of medical care-an arguably costly and inefficient pattern of utilization. However, there are few accurate national data on the prevalence of such usage. This analysis uses the 1998 National Health Interview Survey to estimate the number of Americans who name the ED as their usual source of care, and compares their characteristics with those who have a usual source of care other than the ED. Poverty, lack of insurance, younger age, male gender, and minority race or ethnicity predicted identifying the ED as the usual source of care.