A population-based study was conducted in metropolitan Baltimore in which the short- and long-term prognosis of 283 patients with nontransmural myocardial infarction was compared with that of 953 patients with transmural infraction. After simultaneous adjustment for several variables, the in-hospital case fatality rate was greater for patients with transmural (30.1 percent) than with nontransmural (18.3 percent) infarction (P less than 0.01). However, for patients discharged alive from the hospital and followed up for as long as 10 years, no significant differences in survival were found between the groups with transmural and nontransmural infarction. A multiple adjustment procedure yield 3 year case fatality rates of 27.1 percent and 28.3 percent, respectively, for patients with transmural and nontransmural myocardial infarction surviving the acute phase. These results suggest that the long-term prognosis of patients with nontransmural infarction is as guarded as that of patients with transmural infarction and that attempts to prevent subsequent mortality should be diligently pursued in both groups of patients.