Supported by the Patient Protection and Affordable Care Act of 2010 and as required by the Centers for Medicare & Medicaid Services (CMS), prescribing providers must include their individual (Type 1) National Provider Identifier (NPI) on all prescriptions for Medicare Advantage HMO and PPO members who are covered under the Medicare Part D program. Prescriber identifiers are valuable Part D program safeguards. These identifiers are the only data on Part D drug claims to indicate that legitimate practitioners have prescribed drugs for Medicare enrollees. Without valid prescriber identifiers, efforts made by CMS to determine the validity, medical necessity, or appropriateness of Part D prescriptions and drug claims may be limited.