In a prospective study of old, terminally ill patients who died from various conditions in a general hospital ward, the autopsy established a very high incidence of silent myocardial infarction. Acute myocardial infarction (AMI), clinically not suspected, was demonstrated at autopsy in 20 of 39 cases. 13 AMIs involved only the subendocardial layers. Severe coronary artery stenosis was three times as frequent among the AMI patients as among the others, but recent coronary artery thrombosis was observed in one case only. Clinical and laboratory observations failed to establish the diagnosis of AMI prior to death.