BACKGROUND: The aim of this study was to evaluate the relationship between aortic valve area (AVA) obtained by Doppler echocardiography and outcome in patients with severe asymptomatic aortic stenosis and to define a specific threshold of AVA for identifying asymptomatic patients at very high risk based on their clinical outcome. METHODS AND RESULTS: We included 199 patients with asymptomatic severe aortic stenosis (AVA ≤1.0 cm(2)). The risk of events (death or need for aortic valve replacement) increased linearly on the scale of log hazard with decreased AVA (adjusted hazard ratio 1.17; 95% CI 1.06-1.29 per 0.1 cm(2) AVA decrement; P=0.002). Event-free survival at 12, 24, and 48 months was 63±6%, 51±6%, and 34±6%, respectively, for AVA 0.8 to 1 cm(2); 49±6%, 36±6%, and 26±6%, respectively, for AVA 0.6 to 0.8 cm(2); and 33±8%, 20±7%, and 11±5%, respectively, for AVA ≤0.6 cm(2) (Ptrend=0.002). Patients with AVA ≤0.6 cm(2) had a significantly increased risk of events compared with patients with AVA 0.8 to 1 cm(2) (adjusted hazard ratio 2.22; 95% CI 1.41-3.52; P=0.001), whereas patients with AVA 0.6 to 0.8 cm(2) had an increased risk of events compared with those with AVA 0.8 to 1 cm(2), but the difference was not statistically significant (adjusted hazard ratio 1.38; 95% CI 0.93-2.05; P=0.11). After adjustment for covariates and aortic valve replacement as a time-dependent variable, patients with AVA ≤0.6 cm(2) had a significantly greater risk of all-cause mortality than patients with AVA >0.6 cm(2) (hazard ratio 3.39; 95% CI 1.80-6.40; P<0.0001). CONCLUSIONS: Patients with severe asymptomatic aortic stenosis and AVA ≤0.6 cm(2) displayed an important increase in the risk of adverse events during short-term follow-up. Further studies are needed to determine whether elective aortic valve replacement improves outcome in this high-risk subgroup of patients.