BACKGROUND:Historical data suggesting poor survival in patients with aortic stenosis (AS) who do not undergo treatment are largely confined to patients with severe AS. OBJECTIVES:This study sought to determine the prognostic impact of all levels of native valvular AS. METHODS:Severity of AS was characterized by convention and by statistical distribution in 122,809 male patients (mean age 61 ± 17 years) and 118,494 female patients (mean age 62 ± 19 years), with measured aortic valve (AV) mean gradient, peak velocity, and/or area. The relationship between AS severity and survival was then examined during median 1,208 days (interquartile range: 598 to 2,177 days) of follow-up. Patients with previous aortic valve intervention were excluded. RESULTS:Overall, 16,129 (6.7%), 3,315 (1.4%), and 6,383 (2.6%) patients had mild, moderate, and severe AS, respectively. On an adjusted basis (vs. no AS; 5-year mortality 19%), patients with mild to severe AS had an increasing risk of long-term mortality (adjusted hazard ratio: 1.44 to 2.09; p < 0.001 for all comparisons). The 5-year mortality was 56% and 67%, respectively, in those with moderate AS (mean gradient 20.0 to 39.0 mm Hg/peak velocity 3.0 to 3.9 m/s) and severe AS (≥40.0 mm Hg, ≥4.0 m/s, or AV area <1.0 cm2 in low-flow, low-gradient severe AS). A markedly increased risk of death from all causes (5-year mortality >50%) and cardiovascular disease was evident from a mean AV gradient >20.0 mm Hg (moderate AS) after adjusting for age, sex, left ventricular systolic or diastolic dysfunction, and aortic regurgitation. CONCLUSIONS:These data confirm that when left untreated, severe AS is associated with poor long-term survival. Moreover, they also suggest poor survival rates in patients with moderate AS. (National Echocardiographic Database of Australia [NEDA]; ACTRN12617001387314).