The Medicare Beneficiary Identifier (MBI) uses numbers 0-9 and all uppercase letters except for S, L, O, I, B, and Z.
We exclude these letters to avoid confusion when differentiating some letters and numbers (e.g., between “0” and “O”). Read MLN Matters® Article New MBI Get It, Use It for other helpful information, such as what to do if an MBI changes.
Contact your local Social Security office for further assistance.