To evaluate the diagnostic utility and cost-effectiveness of Doppler echocardiography in adults with symptomatic aortic stenosis, we performed a prospective study in which the need for aortic valve replacement (AVR) was the outcome event. The total sample consisted of 103 adults (mean age, 69 years) undergoing cardiac catheterization for suspected aortic stenosis. Twenty-six patients (25%) were used as a training set to develop a clinical prediction rule. (1) If maximum aortic jet velocity (Vmax) was more than 4.0 m/s, AVR was recommended. (2) If Vmax was less than 3.0 m/s, AVR was not needed. (3) If Vmax was 3.0 to 4.0 m/s and (a) Doppler aortic valve area (AVA) was 1.0 cm2 or less, AVR was recommended, while (b) if Doppler AVA was 1.7 cm2 or greater, AVR was not needed, and (c) if Doppler AVA was 1.1 to 1.6 cm2, consideration of the degree of coexisting aortic insufficiency was necessary. When this rule was applied to the test set (n = 77), the sensitivity was 98%, with a specificity of 89% and a total error rate of 3.9%. The approach could have resulted in cost savings between 24% and 34% compared with an invasive diagnostic approach.