During the period February to December 1990, 52 adult patients were referred to our clinic for evaluation of the presence of the Marfan syndrome. In 24 out of 52 patients the Marfan syndrome was diagnosed. Cardiac abnormalities were found in all patients: mitral insufficiency because of mitral valve prolapse (83%), aortic dilatation (67%), aortic insufficiency (38%), tricuspid valve insufficiency with or without tricuspid valve prolapse (17%) and atrial septal defect (4%). In 3 patients an aneurysm of the ascending aorta was found. Early recognition of the Marfan syndrome is relevant for prevention of the life threatening complication of aortic dissection. In patients with valve abnormalities endocarditis prophylaxis is advised. A Marfan outpatient clinic offers optimal diagnostic possibilities.