"America's Best Hospitals," by US News & World Report, is a sophisticated and influential appraisal of hospital care. Using measures of health care structure, process, and outcome, the report identifies outstanding hospitals in 16 medical specialties through an overall "index of hospital quality." This strong conceptual design, however, has not been adequately implemented because national data sources for all 3 components are severely limited. Most importantly, since there are no national data on process of care, a reputation survey has been used to measure this component of quality. One consequence of reliance on reputation is that a small group of prominent hospitals in each specialty receives such high scores that they automatically rise to the top of the rankings, regardless of structure or outcome score. "America's Best Hospitals" identifies America's best regarded hospitals, but provides limited additional insight into quality. Adequate surveillance and protection of quality in an era of managed care requires measurement systems beyond the scope of existing data and methods.