Anesthesiologists care for patients of all ages, with all conceivable comorbidities, in every kind of health care facility. This leads to a significant challenge in the collection of data to describe the specialty, and in the development of evidence-based performance measures for anesthesiologists. Whereas narrowly defined medical specialties have developed registries based on manual abstraction of clinical data from the medical record (e.g., cardiac surgery), this approach would be prohibitively expensive for anesthesiology, and is unlikely to generate statistically useful data when major adverse outcomes occur a handful of times in tens of thousands of cases. The American Society of Anesthesiologists (ASA) addressed this challenge in 2008 by funding a related organization, the Anesthesia Quality Institute (AQI), to develop the National Anesthesia Clinical Outcomes Registry (NACOR). The technical development of this registry and the approach taken to define the specialty of anesthesiology and the performance of anesthesiologists may serve as a model for other specialty society efforts.