Carolinas Medical Center (the Hospital), located in Charlotte, North Carolina, complied with Medicare billing requirements for 157 of the 240 inpatient claims that we reviewed. However, the Hospital did not fully comply with Medicare billing requirements for the remaining 83 claims, resulting in net overpayments of $331,831 for the audit period. On the basis of our sample results, we estimated that the Hospital received overpayments of at least $1.7 million for the audit period. These errors occurred primarily because the Hospital did not have adequate controls to prevent the incorrect billing of Medicare claims within the selected risk areas that contained errors.