Objective. Homeless individuals frequently use emergency departments (EDs), but previous studies have investigated local rather than national ED utilization rates. This study sought to characterize homeless people who visited urban EDs across the U.S. Methods. We analyzed the ED subset of the National Hospital Ambulatory Medical Care Survey (NHAMCS-ED), a nationally representative probability survey of ED visits, using methods appropriate for complex survey samples to compare demographic and clinical characteristics of visits by homeless vs. non-homeless people for survey years 2005 and 2006. Results. Homeless individuals from all age groups made 550,000 ED visits annually (95% confidence interval [CI] 419,000, 682,000), or 72 visits per 100 homeless people in the U.S. per year. Homeless people were older than others who used EDs (mean age of homeless people 5 44 years compared with 36 years for others). ED visits by homeless people were independently associated with male gender, Medicaid coverage and lack of insurance, and Western geographic region. Additionally, homeless ED visitors were more likely to have arrived by ambulance, to be seen by a resident or intern, and to be diagnosed with either a psychiatric or substance abuse problem. Compared with others, ED visits by homeless people were four times more likely to occur within three days of a prior ED evaluation, and more than twice as likely to occur within a week of hospitalization. Conclusions. Homeless people who seek care in urban EDs come by ambulance, lack medical insurance, and have psychiatric and substance abuse diagnoses more often than non-homeless people. The high incidence of repeat ED visits and frequent hospital use identifies a pressing need for policy remedies. ©2010 Association of Schools of Public Health.