Doppler echocardiographic assessment of the aortic valve area (AVA) using the continuity equation was performed before cardiac catheterization in 100 patients with suspected aortic stenosis. Doppler echocardiographic AVA correlated closely with AVA calculated by the Gorlin equation at catheterization (r = 0.96). However, Doppler echocardiography slightly but systematically underestimated the AVA (p less than 0.001) and did so most markedly in patients with mild stenosis (greater than 1.0 cm2). In multivariate analysis, the difference in AVA by the 2 techniques was positively associated with left ventricular (LV) stroke volume and inversely with the difference between mean catheterization and Doppler gradients, LV ejection fraction and LV outflow tract velocity. Furthermore, the AVA difference also was related to gender, being larger in women. Thus, overall Doppler echocardiography reliably assesses AVA, but the usefulness of the method is somewhat reduced by its underestimation of AVA in mild stenosis. This drawback, however, is usually overcome by taking patients' symptoms into account. Furthermore, lacking a "gold standard," this underestimation need not imply errors of the Doppler echocardiographic method alone, but also may reflect known inaccuracies of the catheterization technique.