Doppler echocardiography allows accurate noninvasive measurement of transaortic velocity and pressure gradient in patients with valvular aortic stenosis. Because pressure gradients vary with transaortic volume flow, calculation of aortic valve area with the continuity equation is essential for complete echocardiographic evaluation of adult patients. The physician and sonographer should be aware of potential technical and physiologic pitfalls in applying Doppler echocardiographic techniques to the evaluation of the adult with aortic stenosis. With proper training and experience, however, the needed data can be obtained reliably and reproducibly. Doppler evaluation of patients with aortic stenosis has improved our understanding of the prevalence and natural history of this disease. In addition, Doppler measures of stenosis severity can be used in a cost-effective manner for clinical decision making regarding the need for valve replacement in symptomatic adults. It now has supplanted the need for invasive measures of stenosis severity in many of these patients.