National Inpatient Hospital Costs: The Most Expensive Conditions by Payer, 2011 presents data from the Healthcare Cost and Utilization Project (HCUP) on costs of inpatient hospital stays in the United States in 2011. It describes the distribution of costs by expected primary payer and illustrates the conditions accounting for the largest percentage of each payer’s hospital costs. The primary payers examined are Medicare, Medicaid, private insurance, and the uninsured. The hospital costs represent the hospital’s cost to produce the services—not the amount paid for services by payers—and they do not include the physician fees associated with the hospitalization. All differences between estimates noted in the text are statistically significant at the .05 level or better.