Age is an important determinant of outcome in acute myocardial infarction (AMI). However, in clinical settings, there is an occasional mismatch between chronological age and physical age. We evaluated whether activities of daily living (ADL), which reflect physical age, also predict complications and prognosis in elderly patients with AMI. Single-center, observational, and retrospective cohort study. Preserved ADL and low ADL were defined according to the scale for independence degree of daily living for the disabled elderly by the Japanese Ministry of Health, Labour, and Welfare. We examined 82 consecutive patients aged ≥75 years with AMI who underwent primary percutaneous coronary intervention. Patients were divided into preserved ADL (n=52; mean age, 81.8±4.8 years; male, 59.6%) and low ADL (n=30; mean age, 85.8±4.7 years; male, 40.0%) groups according to prehospital ADL. The prevalence of Killip class II-IV and in-hospital mortality rate were significantly higher with low ADL compared to that with preserved ADL (23.1% vs 60.0%, P=0.0019; 5.8% vs 30.0%, P=0.0068, respectively). Multivariate analysis showed that ADL was an independent predictor of Killip class II-IV and 1-year mortality after adjusting for age, sex, and other possible confounders (odds ratio 5.11, 95% confidence interval CI 1.52-17.2, P=0.0083; hazard ratio 4.32, 95% CI 1.31-14.3, P=0.017, respectively). Prehospital ADL is a significant predictor of heart failure complications and prognosis in elderly patients with AMI undergoing primary percutaneous coronary intervention, irrespective of age and sex.