The Government Accountability Office (GAO) has estimated that Medicare made almost $48 billion in improper payments in fiscal year 2010, about 38% of Medicare's total payments of $125.4 billion.
In testimony before a House subcommittee on July 28, GAO officials said the Centers for Medicare & Medicaid Services (CMS) faced challenges in designing and implementing internal controls to effectively prevent or detect and recoup improper payments. Improper payments include both overpayments and underpayments (http://tinyurl.com/3l6339x).
Mitka M. Improper Medicare Payments. JAMA. 2011;306(10):1073. doi:10.1001/jama.2011.1254