Nine hundred and seventy eight patients with a first documented myocardial infarction were studied to detect smoking related differences in clinical profile and in-hospital outcome. The distribution of infarct sites differed significantly between smokers and non-smokers. Smokers had higher peak cardiac enzyme concentrations. In spite of this, smokers had a better prognosis than non-smokers. There are important differences between smokers and non-smokers, both in clinical profile and in-hospital outcome, which may reflect a difference in the nature of the underlying coronary disease.