Marfan's syndrome is a disease of collagen microfibrils, the essential 
composition of which, fibrillin, is defective. The coding gene of this large 
protein has been localised on chromosome 15 and partially cloned. Its mutation 
is transmitted in the autosomal dominant mode. It is common, affects many 
organs, especially those rich in collagen. They include the skeleton, the eye 
and cardiovascular system. The prognosis of these patients depends on the degree 
of cardiovascular involvement; the aorta is the principal site of the lesions, 
particularly the aortic root which tends to develop aneurysmal dilatation, then 
dissection, the main cause of premature death of these patients. Mitral valve 
prolapse giving rise to mitral regurgitation may also be observed. Much progress 
has been made is recent years in the management of Marfan's syndrome, especially 
in ultrasound follow-up of the aortic root and the definition of risk factors 
for dissection. In parallel, advances have been made in the treatment, both 
medical with the use of betablockers to try to slow progression to aneurysm, and 
surgical, in replacement of the aorta and aortic valve in time and under optimal 
conditions. Life expectancy is thereby significantly increased. Similar progress 
has been made to allow these patients to have a pregnancy, classically thought 
to carry a high risk of maternal death.