In a retrospective analysis of in-hospital sudden death among patients with acute myocardial infarction, nine of 48 (18.7%) in-hospital deaths after discharge from the coronary care unit were judged "sudden." This group had a significantly prolonged coronary care unit course, a higher incidence of supraventricular and ventricular arrhythmias, and a noticeable incidence of anterior wall myocardial infarction as compared with those of a matched infarct control group. Seventy-seven percent of the sudden-death group had three or more concomitant highrisk factors as compared with only 3% of a matched control group.