OBJECTIVES: There are conflicting views on how hospital mortality with respect to acute myocardial infarction (AMI) has changed since the introduction of thrombolytics and aspirin. Our purpose therefore was to explain this by studying hospital mortality in a nonselected AMI population. and then assess how patients allocated to different treatment groups contribute to overall mortality. DESIGN: Extensive data were collected on all AMI patients admitted to the 10 hospitals in health region 1 (population 850,000) in Norway during a 2 month period. A protocol approved by the European Secondary Prevention Study Group was used. RESULTS: Of the 487 patients, 32% received thrombolytics, 72% aspirin and 22%) none of the treatments. Average in-hospital mortality was 18%. Mortality within the different groups was as follows: no thrombolytics nor aspirin group 35.0% (39/111), aspirin group 13.7%, (30/218), thrombolytics group 17.3% (4/23), and thrombolytics plus aspirin group 11.0% (15/135). The characteristics of the nontreated group compared to the aspirin and aspirin plus thrombolytics groups were more females, older, increased frequency of previous AMI, left ventricular failure, cardiopulmonary resuscitation, history of stroke and peptic ulcer, and electrocardiogram (ECG) findings other than ST elevation. CONCLUSION: In a nonselected AMI population, a patient group receiving neither thrombolytics nor aspirin contributed most significantly to an overall high mortality. This indicates a modest reduction in total AMI mortality after the new therapies were introduced, as the mortality for this group, with a high risk profile, has presumably remained unchanged.