The rate of progression of aortic stenosis (AS) in adults is variable. To determine whether clinical or echocardiographic variables are associated with more rapid hemodynamic progression, we identified 91 AS patients (initial valve area < or = 2.0 cm2) with 2 technically adequate studies separated by > or = 6 months. From the first study, left ventricular dimensions and AS severity were measured by standard Doppler-echocardiographic methods. Each aortic valve was graded for severity of calcification and degree of restricted leaflet motion; the sum of these grades provided a severity index reflecting leaflet pathology. Clinical and electrocardiographic variables were abstracted from medical records. Mean age was 68 years (range 29 to 89) and 61 were women. Initial AS severity ranged from an aortic valve area of 0.6 to 2.0 cm2 (median 1.3 cm2). During a mean follow-up of 1.8 years the aortic valve area decreased 0.04 cm2/year. The patient group with more rapid progression (decrease in aortic valve area > or = 0.1 cm2/year) had a larger proportion of men (p <0.01) and patients with an elevated serum creatinine (p = 0.04), a higher left ventricular mass index (p = 0.01), and a higher severity index (p <0.001). Multivariable regression analysis identified the severity index (direct relation) and the initial aortic valve area (inverse relation) as the only independent variables associated with more rapid progression. In conclusion, the rate of AS progression, although highly variable, is more rapid when leaflet calcification is more marked.