We examined the association between JCAHO accreditation of hospitals, those hospitals' quality of care, and survival among Medicare patients hospitalized for acute myocardial infarction. Hospitals not surveyed by JCAHO had, on average, lower quality (less likely to use aspirin, beta-blockers, and reperfusion therapy) and higher thirty-day mortality rates than did surveyed hospitals. However, there was considerable variation within accreditation categories in quality of care and mortality among surveyed hospitals, which indicates that JCAHO accreditation levels have limited usefulness in distinguishing individual performance among accredited hospitals. These findings support current efforts to incorporate quality of care in accreditation decisions.