To assess the impact of patient age on the use of diagnostic testing in the management of acute myocardial infarction, the authors reviewed the hospital charts of 4,109 patients hospitalized for validated acute myocardial infarction in the Worcester, Massachusetts, metropolitan area during selected years between 1975 and 1986. Older patients were more likely to be female and to have a prior history of angina, hypertension, and diabetes mellitus (p less than 0.001). Acute myocardial infarctions among older patients were more likely to be recurrent, anterior in location, non-Q wave, smaller as reflected by peak creatine kinase levels, and complicated by congestive heart failure, cardiogenic shock, and atrial fibrillation (p less than 0.001). In-hospital mortality was directly related to increasing patient age (p less than 0.001). Patterns of utilization of the following diagnostic tests were examined: Holter monitoring, radionuclide ventriculography, echocardiography, exercise testing, pulmonary artery catheterization, and coronary arteriography. After adjustment for differences in demographic and clinical characteristics and in-hospital mortality, patients aged 65 years and older were significantly less likely to undergo exercise testing than were patients less than age 55. Patients older than age 75 were significantly less likely to undergo radionuclide ventriculography, pulmonary artery catheterization, and coronary arteriography than were younger patients. Sex-specific analyses did not produce results substantially different from those for the overall study population. The results of this community-wide study suggest that among patients hospitalized for acute myocardial infarction, chronologic age may be an independent determinant of utilization patterns of diagnostic testing. These findings suggest the need for a prospective evaluation of this issue, with an additional emphasis placed on the contributions of functional status and noncardiovascular illness to decision-making in the clinical management of acute myocardial infarction patients.