The Centers for Medicare & Medicaid Services (CMS) is responsible for protecting the Medicare program's fiscal integrity and ensuring that it pays only for those services that are its responsibility. Medicare Secondary Payer (MSP) provisions make Medicare a secondary payer to certain group health plans (GHP) and non-group health plans (NGHP), which include auto or other liability insurance, no-fault insurance, and workers' compensation plans. CMS has the right to recover Medicare payments made that should have been the responsibility of another payer, but CMS has not always been aware of these MSP situations. In 2007, Congress added mandatory reporting requirements for GHPs and NGHPs that should enable CMS to be aware of MSP situations. CMS reports that mandatory reporting was pushed back from 2009 to 2011 for some NGHPs and from 2009 to 2012 for others, in part due to concerns raised by the industry. GAO was asked to present background information about the MSP process as it pertains to NGHPs. To do this work, GAO reviewed relevant CMS documentation, including MSP regulations, manuals, and user guides, and conducted an interview with CMS related to mandatory reporting and the MSP process. GAO shared the information in this statement with CMS. CMS provided technical comments, which GAO incorporated as appropriate. GAO has ongoing work examining challenges related to the MSP process for NGHPs.