The Centers for Medicare & Medicaid Services has failed to properly audit private Medicare plans and has not recovered more than $59 million in overpayments, a new report from the Government Accountability Office finds.

This is money that could have been used to provide additional benefits to older Americans or reduce Medicare premiums they pay, according to GAO investigators.

CMS is required under federal law to audit the financial records of at least one-third of plans participating in the Medicare program each year. They are not, however, fulfilling this obligation, the GAO found. Fewer than one-fourth of participating plans were audited in 2001, and just 14% of plans were in 2006, even though Medicare payments to private insurers has steadily increased over that period, GAO researchers said.

Federal officials found significant errors at 41 of the 49 organizations that were audited in 2003. The result was 59 million in overpayments, but no action was taken on the findings, according to the GAO.