BACKGROUND - Because of the health impact of acute myocardial infarction (AMI), substantial resources have been dedicated to improving AMI care and outcomes. Long-term trends in the clinical characteristics, quality of care, and outcomes for AMI over time from the health system perspective in geographically diverse populations are not well known. METHODS AND RESULTS - The present study included 20 550 Medicare patients aged ≥65 years hospitalized in 4 US states (Alabama, Connecticut, Iowa, Wisconsin) with the confirmed primary discharge diagnosis of AMI in 4 periods: 1992-1993 (n=10 292), 1995 (n=5566), 1998-1999 (n=2413), and 2000-2001 (n=2279). With the use of standard quality indicator definitions, treatment of ideal candidates with aspirin and β-blockers within 24 hours after presentation, β-blockers, and angiotensin-converting enzyme inhibitors at discharge was assessed. Multivariable models were constructed to calculate adjusted 1-year mortality. The hospitalized Medicare population with AMI changed substantially during 1992-2001, with increasing age, more comorbidity, and fewer meeting ideal treatment criteria. Although treatment rates increased significantly for all medications, aspirin, β-blockers, and angiotensin-converting enzyme inhibitors were not provided at discharge to 12.6%, 19.7%, and 25.2% of ideal candidates, respectively, in 2000-2001. Crude 1-year mortality increased (27.6%, 28.3%, 30.6%, and 31.0%; P=0.003 for trend, but adjusted mortality declined (compared with 1992-1993, relative risk in 1995=0.94 [95% CI, 0.88 to 1.01]; relative risk in 1998-1999=0.91 [95% CI, 0.85 to 0.98]; relative risk in 2000-2001=0.87 [95% CI, 0.81 to 0.94]). CONCLUSIONS - The quality of care and adjusted 1-year mortality improved significantly for Medicare beneficiaries with AMI during 1992-2001. Nevertheless, fewer were ideal for guideline-based therapy, and absolute mortality remains high, suggesting the need for treatment strategies applicable to a broader range of older patients. © 2006 American Heart Association, Inc.