The most common cardiac defect in Turner syndrome has been described previously as coarctation of the aorta. We have evaluated 35 consecutive patients with Turner syndrome by clinical examination and by M-mode and two-dimensional echocardiography. Twelve patients (34%) had isolated, nonstenotic bicuspid aortic valve. A high correlation (82%) existed between the presence of a systolic ejection click and echocardiographic evidence of a bicuspid aortic valve. These data indicate that bicuspid aortic valve may be the most common cardiac anomaly in Turner syndrome.