This study deals with the five-year survival of 728 myocardial infarction patients who survived the first 28 days after the onset of symptoms. The series was collected by the Helsinki Coronary Register and includes all cases of acute myocardial infarction in the population who were under 66 years of age during the period 1 July 1970 to 30 June 1971. Of the 219 patients who subsequently died, 81.8 per cent died from ischaemic heart disease. The mortality was highest during the first year after the acute phase but did not decrease after the second year. The mortality was higher in patients with a transmural infarction (five-year mortality 34.0%) compared with those with a nontransmural infarction (19.7%). The mortality also was higher for recurrent acute myocardial infractions than for first attacks. The five-year mortality for women was less (20.5%, age-adjusted) than for men (31.6%). This is mainly because of the higher incidence of nontransmural infarcts in women. Acute ischaemic heart disease is more common, more often fatal, and has a poorer long-term prognosis in men than in women in Helsinki. The acute mortality from acute ischaemic heart disease is high in Helsinki when compared with other WHO registers and, in addition, the long-term prognosis seems to be relatively poor in Helsinki.