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BACKGROUND: Symptom and pulmonary function measures of asthma severity are used for severity classification in practice guidelines. However, there is limited methodological evidence in support of their validity and utility. AIM: To validate initial symptom and forced expiratory volume (FEV1) measures of asthma severity with the subsequent risks of exacerbations resulting in emergency room (ER) visits, hospitalisation, and sickness absence from work. In addition, symptom-based measures of change in asthma severity were also evaluated against the concurrent risks of asthma exacerbations. METHOD: A cohort of 361 adult asthmatic patients in general outpatient clinics was studied. At initial interview, frequencies of asthmatic symptoms and nocturnal exacerbations, FEV1, and a severity score combining these measures, were recorded. At re-interview in the third year, the frequencies of asthma exacerbations resulting in ER visits, hospitalisation, and sickness absence, and a self-assessed global measure of change in severity and serially-assessed change in symptom frequencies, were measured. RESULTS: All individual symptom and FEV1 measures were strongly related to the subsequent risks of ER visits, hospitalisation, and sick absence. A severity score of more than 3 (moderate to severe asthma) and self-assessed change in asthma severity were most strongly and significantly associated with greatly increased risks of all outcomes. Individual symptoms and FEV1 measures alone did not show high sensitivities, but the severity score combining these measures gave much more satisfactory validity. Perhaps not surprisingly, self-assessed change in asthma appeared to give the most satisfactory validity. CONCLUSION: These results support the validity and clinical utility of a simple clinical score based on symptom and FEV1 measures, and self-assessed measure of change in severity, for risk classification in contemporary clinical practice guidelines.