Abstract
This paper analyzes private anti-fraud enforcement under the False Claims Act, which compensates whistleblowers for litigating against healthcare providers who overbill the US government. I conduct several case studies of successful whistleblower lawsuits concerning Medicare fraud, pairing new legal data with large samples of Medicare claims. I estimate that deterrence from $1.9 billion in whistleblower settlements generated Medicare cost savings of nearly $19 billion, while imposing low costs on the government. These results suggest private enforcement is a cost-effective way to combat public expenditure fraud.