This study was conducted in 19 hospitals in the metropolitan Seattle area and included 6,270 unselected patients who had acute myocardial infarction (AMI) between January 1988 and April 1991. Hospital mortality was determined and related to patient demographic and clinical characteristics, the use of reperfusion therapies, and to complications after AMI. Thrombolytic therapy or direct coronary angioplasty < 6 hours from symptom onset was used to treat 1,185 (19%) and 524 (9%) patients, respectively. There were 629 (10%) hospital deaths; most occurred during the first 3 days of hospitalization. Factors affecting mortality after admission included: recurrent chest pain, recurrent AMI, development of heart failure, and the occurrence of stroke. After adjustment for age, treatment with thrombolytic therapy or direct angioplasty had no independent effect on reducing the overall mortality rate. Hospital mortality rates for AMI have improved considerably since 1970, although recurrent myocardial ischemic events continue to have an adverse effect on outcome. The current use of reperfusion treatments has had minimal causal impact on overall mortality rates, principally because less than one third of patients, who are relatively "low risk," are eligible and receive these treatments.