BACKGROUND: Electron-beam computed tomography (EBCT) is used to measure coronary calcification but not for aortic valve calcification (AVC). Its accuracy, association with aortic stenosis (AS) severity, and diagnostic and prognostic value with respect to AVC are unknown. METHODS AND RESULTS: In 30 explanted aortic valves, the AVC score by EBCT (1125+/-1294 Agatston units [AU]) showed a strong linear correlation (r=0.96, P<0.0001) with valvular calcium weight (653+/-748 mg) by pathology that allowed estimation of calcium weight as AVC score/1.7, with a small standard error of the estimate (53 mg). In 100 consecutive clinical patients, we measured AVC by EBCT and AS severity by echocardiographic aortic valve area (AVA). The AVC score was 1316+/-1749 AU (range 0 to 7226 AU). Intraobserver and interobserver variabilities were excellent (4+/-4% and 4+/-10%, respectively). AVC and AVA were strongly associated (r=0.79, P<0.0001) but had a curvilinear relationship that suggested that AVC and AVA provide complementary information. AVC score > or =1100 AU provided 93% sensitivity and 82% specificity for diagnosis of severe AS (AVA <1 cm2), with a receiver operator characteristic curve area of 0.89. AVC assessment by echocardiography was often more severe than by EBCT (P<0.0001). During follow-up, 22 patients either died, developed heart failure, or required surgery. With adjustment for age, sex, symptoms, ejection fraction, and AVA, the AVC score was independently predictive of event-free survival (risk ratio 1.06 per 100-AU increment [1.02 to 1.10], P<0.001), even after adjustment for echocardiographic calcifications. CONCLUSIONS: AVC is accurately and reproducibly measured by EBCT and shows a strong association and diagnostic value for severe AS. The curvilinear relationship between AVC and AVA suggests these measures are complementary, and indeed, AVC provides independent outcome information. Thus, AVC is an important measurement in the evaluation of patients with AS.