Despite national concern about homeless veterans, there has been little examination of their use of emergency department (ED) services. This study examines factors related to the use of ED services in the Veterans Affairs (VA) healthcare system, where insurance is not a barrier to ambulatory healthcare. National VA administrative data from fiscal year 2010 are used to describe the proportions of ED users among homeless and domiciled VA patients. A case-control design is then used to compare homeless ED and non-ED users on sociodemographic and clinical correlates, as well as use of ambulatory care and psychotropic medications. Sixteen percent of domiciled VA patients used EDs at least once during the year and 1% were frequent ED users (> 4 ED visits) compared to 45% of homeless VA patients, 10% who were frequent ED users. Among homeless VA patients, those who used EDs were more likely to have a range of psychiatric and medical conditions, and had more service visits and psychotropic medication prescriptions than non-ED users. Multivariate analyses suggest their risk for psychiatric and medical conditions increase their likelihood of using ED services. The high rate of ED use among homeless veterans is associated with significant morbidity, but also greater use of ambulatory care and psychotropics suggesting their ED use may reflect unmet psychosocial needs.