MBI stands for Medicare Beneficiary Identifier. It is an 11-character combination of letters and numbers that is randomly generated and assigned to each person with Medicare. The MBI replaced the Social Security Number (SSN)-based Health Insurance Claim Numbers (HICNs) on all Medicare cards to offer better identity protection. The MBI is confidential like the SSN and should be protected as Personally Identifiable Information. It is required for all Medicare transactions, including claim submission, appeals, audits, and eligibility transactions. The MBIs characters are "non-intelligent" and do not have any hidden or special meaning. The MBI contains only numbers and uppercase letters, and it does not use the letters S, L, O, I, B, and Z to avoid confusion between some letters and numbers.