375 consecutive patients below 65 years who had an acute myocardial infarction (AMI) took part in a randomised rehabilitation and secondary prevention trial (part of a W.H.O.-coordinated project) designed to study the effects of a multifactorial intervention programme on morbidity, mortality, return to work, &c. After three years' follow-up the cumulative coronary mortality was significantly smaller in the intervention group than in the controls (18.6% versus 29.4%, p = 0.02). This difference was mainly due to a reduction of sudden deaths in the intervention group (5.8% versus 14.4%, p less than 0.01). The reduction was greatest during the first six months after AMI. 18.1% in the intervention group and 11.2% in the controls (p less than 0.10) presented with non-fatal reinfarctions. The number of patients with new Q-QS findings at the end of the three years was, however, almost the same in both groups. The results suggest that organised aftercare during the first six months after AMI with special emphasis on optimum medical control and health education contributes significantly to a reduction in the number of sudden deaths.