Book excerpt: GAO has designated Medicare as a high-risk program, in part because the program's size and complexity make it vulnerable to fraud, waste, and abuse. In 2013, Medicare financed health care services for approximately 51 million individuals at a cost of about $604 billion. The deceptive nature of fraud makes its extent in the Medicare program difficult to measure in a reliable way, but it is clear that fraud contributes to Medicare's fiscal problems. More broadly, in fiscal year 2013, Centers for Medicare & Medicaid Services (CMS) estimated that improper payments—some of which may be fraudulent—were almost $50 billion.