The role of medical liability reform is an ongoing and active debate, particularly with respect to its impact on controlling the escalating costs of health care. One key premise of cost control measures is reducing the practice of defensive medicine. This study generated an annual estimate of $55.6 billion, or 2.4% of total health care spending, attributed to the many highlighted elements of liability system costs. The analysis points to defensive medicine accounting for $46 billion of that estimate, though limited by the poor quality of the evidence available to generate it. The authors discuss their findings and suggest potential improvements that may result from current health reform policies. This study is part of a special issue on medical malpractice and errors in Health Affairs. An accompanying editorial [see link below] discusses features highlighted from this issue in the context of current health reform. A past AHRQ WebM&M perspective discussed the unintended consequences of Florida Medical Liability Legislation.