A longitudinal population study of 1,462 women, aged 38-60 years at entry, was begun in Gothenburg, Sweden, in 1968-1969. This paper deals with the first 12-year follow-up period. In univariate analysis, peak expiratory flow showed a significant negative correlation with the 12-year incidences of myocardial infarction, electrocardiographic changes suggesting ischemic heart disease, stroke, and death. The association with incidence of myocardial infarction, stroke, and death remained in multivariate analysis, and was independent of age, body height, body mass index, adipose tissue distribution, chest deformity, history of pulmonary disease, smoking habit, serum cholesterol concentration, serum triglyceride concentration, systolic blood pressure, diabetes, and physical activity. The findings indicate that measuring peak expiratory flow is a simple procedure to identify women with an increased risk of cardiovascular disease or death. It seems urgent to find out what preventive measures might be taken as a consequence of these observations.