Data on all patients with myocardial infarctions treated in the ten hospitals in Health region 1 in Norway were extensively analysed. Of the 487 patients with the diagnosis acute myocardial infarction, 429 (88%) had definite or suspected acute myocardial infarction; 440 (90%) were treated in an intensive care unit. Average age was 70 years, for men 68 years and for women 75 years, and 69% of the patients suffered their first acute myocardial infarction. Within six hours 59% of the patients were admitted to hospital and within 12 hours 76%. On admission, 58% of the patients had an electrocardiogram showing ST elevation or bundle branch block. The remainder showed other findings, of which ST depression was the most frequent (23%). In-hospital mortality was 18% and of those discharged 10% died within six months. It is concluded that the true acute myocardial infarction population differs from the population of patients in clinical trials as follows: higher age, longer delay before admission to hospital, a different distribution of EGG findings, and higher mortality.