The noninvasive measurement of aortic valve area by use of the continuity equation has been proposed as an accurate method for determining the severity of aortic stenosis. In 32 patients (mean age 64 +/- 14 years) with proven aortic stenosis and without significant regurgitation, aortic valve areas derived by the Gorlin equation from cardiac catheterisation data were compared with valve areas calculated from the continuity equation using Doppler echocardiography. There was a close correlation between Doppler and catheter derived aortic valve areas (r = 0.87, SEE = 0.17 cm2). The interobserver error for aortic valve area measurement in 20 patients was 9.0 +/- 6.8%. The specificity of this method for critical aortic stenosis (aortic valve area less than 0.75 cm2) was 73% and the sensitivity 88%. We conclude that in an adult, predominantly elderly population with calcific aortic stenosis, this Doppler echocardiographic method is reproducible and can be used accurately to derive aortic valve area.