Follow-up data for 515 survivors of acute non-Q wave myocardial infarction were categorized according to mortality: 1) between hospital discharge and 3 months after infarction (early), and 2) between 3 and 12 months after infarction (late). The mortality rate decreased steadily for the first 3 months and was constant thereafter. There were 25 early and 32 late deaths. After adjustment for the longer time associated with the 3 to 12 month period, the relative risk per unit time of early as compared with late mortality was 2.64. Risk factors for early mortality were different from those that predicted late mortality. Independent predictors of mortality between hospital discharge to 3 months after infarction were ST segment depression that persisted during hospitalization (p less than 0.0001), in-hospital reinfarction (p = 0.0006) and a history of congestive heart failure (p = 0.0255). Persistent ST depression and in-hospital reinfarction had neither a univariate nor an independent association with 3 to 12 month mortality. Age (p less than 0.0001), reinfarction between discharge and 3 months (p = 0.0147) and diabetes (p = 0.0404) were independently associated with late mortality. Early mortality was only 0.5% (1 of 199) in patients with no ST depression at either baseline or discharge (group 1); 4.8% (8 of 168) in those with ST depression at exactly one time point (group 2) and 13.7% (16 of 117) in those who had ST depression present at both time points (group 3). All pairwise differences were significant (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)