We investigated the morphology of the stenotic aortic valve, the progression of the stenosis, and the onset and progression of aortic regurgitation (AR) in patients with congenital aortic valvular stenosis (AVS). The medical records of 278 patients with AVS were reviewed, with the patients with concomitant lesions besides AR excluded. Very mild aortic stenosis was defined as a transvalvular Doppler peak systolic instantaneous gradient (PSIG) less than 25 mmHg, mild stenosis as 25-49 mmHg, moderate stenosis as 50-75 mmHg, and severe stenosis as more than 75 mmHg. The mean age of the patients was 4.9 +/- 4.3 years (range, 3 days to 15 years), and 203 (73%) were male. The number of the cusps was determined with two-dimensional echocardiography in 266 patients (95%): unicuspid in 3 patients (1%), bicuspid in 127 patients (48%), and tricuspid in 136 patients (51%). A total of 192 of all patients were followed for 2 months to 14.6 years (mean 4.2 +/- 3.3 years) with medical treatment alone. Among 72 patients with very mild stenosis at initial echocardiographic examination, 20% had mild, 3% moderate, and 1% severe stenosis after a mean period of 3.7 years. In 70 patients with mild stenosis at initial echocardiographic examination, 28% had moderate and 9% severe stenosis after a mean period of 5 years. Among 44 patients with moderate stenosis at initial echocardiographic examination, 36% had severe stenosis after a mean period of 3.7 years. Among 192 patients, 40% had AR (3% trivial, 28% mild, and 9% moderate) at initial echocardiographic examination. After a mean period of 4.2 years, 58% of the patients had AR (13 % trivial, 25% mild, 16% moderate, and 4% severe). There was not statistically significant difference between catheterization peak systolic gradients (47 +/- 16 mmHg) and Doppler estimated mean gradients (45 +/- 9 mmHg) (p = 0.53), whereas Doppler PSIGs (74.9 +/- 15.7 mmHg) were higher than catheterization peak systolic gradients (p < 0.0001) in 25 patients who were studied in the catheterization lab. Patients with very mild stenosis may be followed with a noninvasive approach every 1 or 2 years, and an annual follow-up is suggested for patients with mild stenosis. Nearly one-third of patients with moderate stenosis at initial echocardiographic examination had severe stenosis after a mean period of 3.7 years. Therefore, we recommend, that patients with moderate stenosis undergo noninvasive evaluation every 6 months. Doppler estimated mean gradient is very useful in predicting the need for intervention in children with AVS.