A population-based approach to monitoring quality of care combining small-area analysis and outcomes assessment is proposed. While adverse outcomes due to poor surgical technique have long been targeted for quality-of-care review, in this study, giving similar attention to adverse outcomes produced by high rates of interventions is proposed. A population-based approach will strengthen traditional review efforts that currently begin and end at the hospital door. Excluded from these reviews have been questions such as the following: Should the procedure have been performed in the first place? Did the benefits outweigh the risks? Were there other patients not operated on who might have benefited more? Traditional approaches can identify less competent hospitals or practitioners: population-based approaches can identify the surgical enthusiasts who may pose equal risks to the populations of the areas they serve. Applying a population-based approach to review of coronary artery bypass graft surgery for Medicare patients in five cities in the United States demonstrates that at least as many deaths could have been prevented by decreasing surgical rates to the U.S. average as by improving the technical quality of care with which the procedure was performed. A similar population-based analysis of complications (as judged by re-admissions within 30 days of surgery) associated with hysterectomy across regions of Manitoba, Canada, is presented. In summary, negligent acts in the delivery of health care in institutions are rare and are difficult to detect because medicine is an inexact science and because adverse outcomes are more likely in high-risk patients, regardless of the quality of care. However, from a population perspective, adverse events are predictable, occur relatively frequently, and are directly related to the frequency of a population's exposure to surgical intervention. Efforts to improve quality of care could be made more effective by including the rates at which populations are exposed to treatments and the technical quality of care delivered.