We have evaluated 46 patients with Turner syndrome by clinical examination, M-mode and two-dimensional echocardiography, dynamic exercise testing and 24 h Holter monitoring. Twelve patients (26.1%) had mitral valve prolapse and 7 patients (15.2%) had isolated non stenotic bicuspid aortic valve. Aortic root dilation was present in 2 patients (4.3%). Our data indicate that incidence of mitral valve prolapse is significantly higher in Turner syndrome than in the general population (P less than 0.025).