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 < 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 < 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 < 0.01). Relative risks for early mortality were 27.2 (group 3 versus group 1), 2.9 (group 3 versus group 2) and 9.5 (group 2 versus group 1). In contrast, late mortality was 5.0% in group 1, 5.6% in group 2 and 9.9% in group 3 (p > 0.1 for all pairwise comparisons). In-hospital reinfarction was significantly associated with increased early mortality (relative risk 4.6) and nonsignificantly associated with decreased late mortality (relative risk 0.55). It is concluded that 1) in patients with non-Q wave myocardial infarction, ST depression that persists through hospitalization and in-hospital reinfarction are major risk factors for mortality at 3 months but not for mortality between 3 and 12 months; 2) after 3 months of decreasing risk, the mortality rate in these patients remained constant for the next 9 months; and 3) with only one early death among 199 patients with non-Q wave infarction and no in-hospital ST depression, these patients are at extremely low risk and do not appear to require early angiography.