A prospective follow-up study was carried out to investigate the relation between smoking and risk of death after an acute myocardial infarction. The study consisted of male patients under the age of 65 years, who had had an acute myocardial infarction between 1972 and 1975 in North Karelia, Finland. Of these patients, 888 survived the first six months after the acute infarction and were followed-up for three years after the infarction with regard to their deaths. The cumulative all-causes mortality rate of the patients who were still smoking six months after the acute myocardial infarction was 1.7 times that of the patients who had stopped smoking within the first six months. There was a dose-response relation between the number of cigarettes smoked daily and the mortality. The impact of smoking was greatest in the subgroups of patients with an otherwise good prognosis. We estimated that 28 per cent of the deaths in the whole group of initial smokers was attributable to continuing smoking after the infarction. On the basis of these findings we suggest that the anti-smoking advice should be an important part of the modern comprehensive care of patients with an acute myocardial infarction.