In the United States, patient usage of costly emergency departments (EDs) has been portrayed as a major factor contributing to health care expenditures. The homeless are associated with ED frequent users, a population often blamed for inappropriate ED use. This study examined the characteristics and costs associated with homeless ED frequent users. A retrospective cross-sectional review of hospital records for ED visits in 2006 at an urban academic medical center was performed. Frequent users were defined as having greater than 4 ED visits in one year. Homeless status was determined by self-report and review by an interdisciplinary team. A total of 5440 (8.9%) ED visits were made by 542 frequent users, 74 (13.7%) of whom were homeless and made 845 ED visits. Homeless frequent users had a median age of 47 years (39-56 interquartile range), were predominantly male (85.1%), and insured by Medicaid (59.5%). Most (44.2%) visits by homeless frequent users occurred between 1500-2259 hours and had an Emergency Severity Index of Level 3 (55.5%). Sixty-four percent of visits resulted in homeless patients being discharged back to the street; only 4.0% had a specific discharge plan addressing homelessness. Total charges and payments for all homeless frequent users were $4,812,615 and $802,600, respectively. The single top frequent user accrued charges of $482,928. ED frequent users are disproportionately homeless and their costs are significant. ED discharge planning should address the additional risks faced by homeless individuals. ED-based interventions that specifically target the most expensive homeless frequent users may prove to be cost-effective.