We assessed progressive stenosis of the aortic valve in 11 adult patients (mean age of 48 years) with aortic stenosis who had undergone two cardiac catheterizations without intervening aortic valve surgery. The mean time between cardiac catheterization was 59 months (range 20 to 133). No patients had mitral valve disease. Two patients had coronary artery disease. The results showed that progressive stenosis of the aortic valve occurred in 10 of 11 patients with a significant decrease in the calculated mean aortic valve area from 1.2 +/- 0.2 sq cm to 0.7 +/- 0.1 sq cm (P less than 0.005); a significant increase in mean left ventricular peak systolic pressure from 149 +/- 8 mm Hg to 199 +/- 3 mm Hg (P less than 0.01), and a significant increase in mean left ventricular aortic pressure gradient from 31 +/- 4 mm Hg to 75 +/- 13 mm Hg (P less than 0.005). On an individual basis, the change in left ventricular pressure and the left ventricular-aortic gradient did not always reflect the decrease in aortic valve area because of variations in cardiac output. The shortest period of time in which progression of aortic stenosis occurred was 27 to 29 months. Thus, progressive stenosis of the aortic valve occurs in adults with isolated aortic valvular stenosis. Significant decrease in the aortic valve area can develop in as short a period as 27 to 29 months.