There is renewed national attention on the consequences of gun violence in the U.S. This study presents new information on the prevalence and cost of emergency department visits and inpatient hospital stays in U.S. hospitals for injuries associated with armed assault. In 2010, young adult men, residents of low income areas, and the uninsured had the highest rates of use. The total hospital cost of such injures is very high, equivalent to the cost of the Medicaid program one state. The prevention of firearm assaults should receive increased attention as a high public health priority.