All nations seek to reduce the human toll from medical error, but variations in legal and institutional structures guide those efforts into different trajectories. This article compares legal and institutional responses to patient safety problems in the United States and Japan, addressing developments in civil malpractice law (including discoverability of internal hospital documents), administrative practice (including medical accident reporting systems), and - of particular significance in Japan - criminal law. In the U.S., battles over rules of malpractice litigation are fierce; tort law occupies center stage. The hospital accreditation process plays a critical role in medical quality control, and peer review is relatively well developed. In Japan, although malpractice litigation is increasing, malpractice premiums (stabilized by nationwide risk pooling without regard to medical specialty) do not pinch the profession to a comparable degree. Pressures on hospitals from civil litigation and from hospital accreditors are less stringent; peer review and professional discipline are weak. Nonetheless, democratic societies demand public accountability, and the relative frailty of other structures regulating medicine has made the criminal justice system, its proceedings amplified by the media, into an accountability mechanism of last resort. Few would contend police and prosecutors are well suited for the medical quality control role into which their criminal code enforcement responsibility has thrust them. Regarding two points, however, the criminal justice system's involvement in medical cases has offered Japan unqualified benefits. First, it has served as a national wake-up call, helping motivate the medical profession to undertake internal system improvements and to assist in the health ministry's innovative "model project" for neutral expert investigation of medical accidents. Second, under criminal law's looming presence, and with hospital whistleblowers and unforgiving media on patrol, Japanese physicians' and hospitals' entrenched practice of systematic deception of patients about medical harm is likely on the wane.