Master Beneficiary Summary File (MBSF) Base

The MBSF base segment includes beneficiary enrollment information, (A/B/C/D). Medicare Advantage (Part C) and the Prescription Drug Program (Part D) plan enrollment information is included.

What does this file include? (variable highlights)

  • State, county annual SSA codes
  • State, county monthly FIPS codes
  • Zip code, State and County
  • Date of birth, date of death
  • Race
  • Reason for entitlement
  • Monthly enrollment for each part of the Medicare program, A/B/C/D
  • Dual eligible status
  • Part C plan and enrollment information
  • Part D plan and enrollment information
  • Part D low income cost sharing

Special considerations

Availability of this file

CY 1999-2022

Date Requests Can Be Accepted for Upcoming Releases:

CY 2023 available 11/2024

The Part D variables in the Base segment are available for years 2006 and forward only.

See what is in this file