Medicare, an important payer for hospitals, reimburses hospitals for inpatient stays using Diagnosis Related Groups (DRGs). Many private insurers also use the DRG methodology to reimburse hospitals for their services. Therefore, those blood service organizations that bill Medicare directly require an understanding of the DRG system of payment to enable them to bill Medicare correctly, and in order to be certain they are adequately reimbursed. Blood centers that do not bill Medicare directly need to understand how hospitals are reimbursed for blood and blood components as this affects a hospital's ability to pay service fees related to these products. This review presents a detailed explanation of how hospitals are reimbursed by the Centers for Medicare and Medicaid Services (CMS) for Medicare inpatient services, including blood services. © 2009 American Association of Blood Banks.