In 29 initially asymptomatic patients with aortic stenosis followed for an average of 18 months, patients with a N-terminal pro-brain natriuretic peptide (NT-pro-BNP) level above the normal range at baseline were more likely to develop symptoms during follow-up compared with patients with NT-pro-BNP within normal limits. The average increase in NT-pro-BNP per year was greater for patients who developed symptoms compared with patients who remained asymptomatic. Aortic valve area, peak aortic velocity, and the ejection fraction were less reliable predictors of symptom onset. Measurement of NT-pro-BNP in addition to clinical assessment and echocardiography may allow more reliable follow-up and timing of valve replacement for aortic stenosis.