We examined, in age subsets, 2643 patients with acute myocardial infarction. Clinical features and 1 year morbidity and mortality were compared in 203 young patients (70 years). Ninety-two percent of young patients were men, and a family history of premature coronary artery disease was more common in young patients (41% compared with 28% of middle-aged and 12% of elderly patients). More young patients were currently smoking cigarettes (82% compared with 56% of middle-aged and 24% of elderly patients), and only 8% of young patients had never smoked. Previous myocardial infarction and history of angina pectoris or congestive heart failure were less common (p < .001) in the young patients than in middle-aged and elderly patients. In-hospital mortality was only 2.5% for young patients, compared with 9.0% in middle-aged and 21.4% in elderly patients (both p < .001). Postdischarge 1 year mortality was also strikingly low in young patients, at 2.6% compared with 10.3% in middle-aged and 24.4% in elderly patients. The incidence of reinfarction during the 1 year of follow-up was similar in all subsets. The statistical significance of 65 variables as predictors of 1 year mortality and reinfarction was tested and the following found to be significant (p < .05): hospital discharge on antiarrhythmic drugs, digoxin, or diuretics; history of previous myocardial infarction or congestive heart failure; chest x-ray findings of heart failure; low ejection fraction; and atrial fibrillation. Thus, young patients entering the hospital have an excellent 1 year prognosis, but those with prior infarction in whom there are selected abnormal findings at hospital discharge comprise a subgroup that may benefit from early aggressive management.