Ventilatory function as a predictor of fatal stroke. OBJECTIVE--To investigate the relation between ventilatory function and subsequent mortality due to cerebrovascular disease. DESIGN--Prospective longitudinal study. SUBJECTS--A total of 18,403 male civil servants aged 40-64 years at entry examination for the Whitehall study. MAIN OUTCOME MEASURE--Mortality from cerebrovascular disease (ICD8 430-438) after 18 years of follow up. RESULTS--In all, 262 men with sinus rhythm at entry died due to stroke during the 18 years of follow up. Compared with men with a forced expiratory volume in one second of greater than or equal to 3.5 litres those with a value of less than 3.0 litres were almost twice as likely to die of cerebrovascular disease (rate ratio adjusted for age and systolic blood pressure = 1.88, 95% confidence interval 1.32 to 2.69). This increased risk occurred within each tertile of systolic blood pressure. Nested case-control analyses were used to control precisely for confounding effects of age, height, and smoking (by matching) and employment grade and physiological risk factors (by modelling). The effect of forced expiratory volume in one second was independent of age, height, smoking habits, employment grade, blood pressure, weight, cholesterol concentration, glucose tolerance, electrocardiographic abnormalities, history of chest pain, and history of intermittent claudication. CONCLUSIONS--Measurements of ventilatory function may assist clinical decisions about whether to treat mild hypertension. Impaired ventilatory function and stroke may share common causes. 