Context: Issues of cost and quality are gaining importance in the delivery of medical care, and whether quality of care is better in teaching vs nonteaching hospitals is an essential question in this current national debate. Objective: To examine the association of hospital teaching status with quality of care and mortality for fee-for-service Medicare patients with acute myocardial infarction (AMI). Design, Setting, and Patients: Analysis of Cooperative Cardiovascular Project data for 114411 Medicare patients from 4361 hospitals (22354 patients from 439 major teaching hospitals, 22493 patients from 455 minor teaching hospitals, and 69564 patients from 3467 nonteaching hospitals) who had AMI between February 1994 and July 1995. Main Outcome Measures: Administration of reperfusion therapy on admission, aspirin during hospitalization, and β-blockers and angiotensin-converting enzyme inhibitors at discharge for patients meeting strict inclusion criteria; mortality at 30, 60, and 90 days and 2 years after admission. Results: Among major teaching, minor teaching, and nonteaching hospitals, respectively, administration rates for aspirin were 91.2%, 86.4%, and 81.4% (P<.001); for angiotensin-converting enzyme inhibitors, 63.7%, 60.0%, and 58.0% (P<.001); for β-blockers, 48.8%, 40.3%, and 36.4% (P<.001); and for reperfusion therapy, 55.5%, 58.9%, and 55.2% (P=.29). Differences in unadjusted 30-day, 60-day, 90-day, and 2-year mortality among hospitals were significant at P<.O01 for all time periods, with a gradient of increasing mortality from major teaching to minor teaching to nonteaching hospitals. Mortality differences were attenuated by adjustment for patient characteristics and were almost eliminated by additional adjustment for receipt of therapy. Conclusions: In this study of elderly patients with AMI, admission to a teaching hospital was associated with better quality of care based on 3 of 4 quality indicators and lower mortality.