BACKGROUND: Guidelines recommend that patients with myocardial infarction (MI) receive equal care regardless of age. However, withholding treatment may be justified in elderly and frail patients. This study aimed to investigate trends in treatments and outcomes of older patients with MI according to frailty. METHODS AND RESULTS: All patients aged ≥75 years with first-time MI during 2002 to 2021 were identified through Danish nationwide registries. Frailty was categorized using the Hospital Frailty Risk Score. One-year risk and hazard ratios (HRs) for days 0 to 28 and 29 to 365 were calculated for all-cause death. A total of 51 022 patients with MI were included (median, 82 years; 50.2% women). Intermediate/high frailty increased from 26.7% in 2002 to 2006 to 37.1% in 2017 to 2021. Use of treatment increased substantially regardless of frailty: for example, 28.1% to 48.0% (statins), 21.8% to 33.7% (dual antiplatelet therapy), and 7.6% to 28.0% (percutaneous coronary intervention) for high frailty (all P-trend <0.001). One-year death decreased for low frailty (35.1%–17.9%), intermediate frailty (49.8%–31.0%), and high frailty (62.8%–45.6%), all P-trend <0.001. Age-and sex-adjusted 29-to 365-day HRs (2017–2021 versus 2002–2006) were 0.53 (0.48–0.59), 0.62 (0.55–0.70), and 0.62 (0.46–0.83) for low, intermediate, and high frailty, respectively (P-interaction=0.23). When additionally adjusted for treatment, HRs attenu-ated to 0.74 (0.67–0.83), 0.83 (0.74–0.94), and 0.78 (0.58–1.05), respectively, indicating that increased use of treatment may account partially for the observed improvements. CONCLUSIONS: Use of guideline-based treatments and outcomes improved concomitantly in older patients with MI, irrespective of frailty. These results indicate that guideline-based management of MI may be reasonable in the elderly and frail.