Nineteen patients with types I and III Ehlers-Danlos syndrome were hospitalized at our institution between 1973 and 1978. Chest roentgenogram, electrocardiogram, and echocardiogram were done; 11 patients underwent cardiac catheterization. Thirty-five cardiac or great vessel abnormalities were detected. Fifteen patients had nitral valve prolapse; six also had tricuspid valve prolapse. Dilatation of the aortic root or extasia of the sinuses of Valsalva, or both, occurred in six patients. Dilatation of the pulmonary artery and annulus caused pulmonary regurgitation in one patient. Congenital heart defects included bicuspid aortic valve (two), pulmonary valvular stenosis (one), ventricular septal defect (two), and an atrial septal defect (one). The apparent high prevalence of cardiovascular abnormalities in hospitalized patients with types I and III Ehlers-Danlos syndrome necessitates a careful cardiovascular evaluation. Conversely, Ehlers-Danlos syndrome types I and III should be excluded in patients with mitral or tricuspid valve prolapse, great vessel dilatation, and congenital heart defects.