Three-hundred and seventy-five unselected patients below 65 years of age and with acute myocardial infarction participated in a controlled investigation aimed at studying the effects of a multifactorial intervention programme on morbidity, mortality and risk factor control. After ten years' follow-up the significantly lower sudden death and coronary mortality observed three years after myocardial infarction still persisted in the intervention group (188 patients) compared with the control group (187 patients). The incidence of sudden death in the intervention group was 12.8% compared with 23.0% in the controls (P = 0.01). The incidence of coronary mortality was 35.1% and 47.1%, respectively (P = 0.02). No significant difference was found in the number of patients with clinical non-fatal reinfarctions (25.6% and 19.3%, respectively). During the first year, when the mortality difference was most marked, the use of beta blockers was not significantly different between the groups. The results suggest that with a multifactorial intervention programme which starts early after the infarction and lasts for years a significant long-term reduction in sudden deaths and coronary mortality can be attained.