The Marfan syndrome (MFS) is one of the most common (1:3000-1:4000) heritable connective tissue disorders. It's still a rarely diagnosed syndrome, especially in childhood. Near all cases MFS results from mutations in the fibrillin-1 (FBN1) gene on chromosome 15q21.1, which encodes for the glycoprotein fibrillin. The FBN1 gene is a large protein that can cause more than 500 mutations and molecular examinations, finally confirming the diagnosis, are conducted extremely rare. We present prospective data concerning 66 patients with clinically-diagnosed MFS who have been controlled in Department of Pediatric Cardiology and Congenital Heart Diseases Medical University in Gdansk in 2000 - 2010. 29 patients (44%) had mitral valve regurgitations, 19 (29%) aneurysmal dilatation of the aorta, 13 (20%) had both these irregularities. In 7 cases (11%) diagnosis of mitral valve prolapse preceded appearance of an aneurysmal dilalation of the aortic bulb. During the observation 11 patients (17%) underwent cardiosurgical procedures for the sake of stopping crucial progressive mitral valve dysfunction and/or aneurysmal dilatation of the aortic bulb, which threatened with a rupture of aortic aneurysm. In 39 cases (59%) prophylactic treatment with beta - blockers was administered. The patients with MFS need a multidisciplinary system of care and the psychological supporting. The cardiosurgical treatment, which nowadays is bringing better results, due to the technological advancements is a new hope for this patient population.