State Medical Boards that license and discipline physicians play an important and insufficiently studied role in medical quality assurance. Only Boards can limit or remove a physician's license to practice, and this project used six case studies and available national data to assess their role in disciplining physicians. The main disciplinary process is complaint-driven investigation and administrative prosecution. Cases proceed through intake, investigation, pre-hearing preparations, and hearings, and problems and performance vary by stage. Several methods appear to improve the throughput and timeliness of conventional discipline, and Boards are experimenting with some promising alternatives to conventional practice.