OBJECTIVE--To assess the pattern and progression of aortic valve dysfunction by serial Doppler echocardiographic examinations in ambulatory adult patients with congenital bicuspid aortic valve. DESIGN AND SETTING--Retrospective analysis of patients referred for Doppler echocardiography over a four year period. SUBJECTS--Fifty one adult patients with echocardiographic diagnosis of congenital bicuspid aortic valve had serial Doppler echocardiographic studies at least six months apart. There were 40 men and 11 women with a mean age of 36 years. MAIN OUTCOME MEASURE--Doppler echocardiographic values of aortic valve dysfunction. Cardiac events including endocarditis and aortic valve replacement were also evaluated. RESULT--Coarctation was present in five patients. 31 (61%) patients had a functionally normal bicuspid aortic valve defined as a mean gradient < 25 mm Hg and mild regurgitation. Significant aortic regurgitation was present in 15 patients (moderate in 12 and severe in three). Three patients had isolated aortic stenosis and two patients had combined aortic valve dysfunction. At a median follow up of 21 months (range six to 46 months), six patients had aortic valve surgery (one for aortic stenosis, three for aortic regurgitation, and two for endocarditis). Only 22 patients (43%) continued to have a functionally normal aortic valve. CONCLUSION--In this cohort of fairly young patients, aortic regurgitation is more common than aortic stenosis. Progression of aortic valve dysfunction occurs in patients with pre-existing valve dysfunction and even in those with normal aortic valve function at the initial echocardiographic examination.