Marfan syndrome is usually inherited as an autosomal dominant trait with high degree of penetrance. It is caused by an abnormal fibrillin gene located on chromosome 15q. Cardiovascular involvement in Marfan syndrome has been overstressed, although very little attention has been given to obstetric complications. Marfan syndrome may be responsible of cervical incompetence, abnormal placental site and post partum haemorrhagic complications. A 22-year-old woman with Marfan syndrome had mitral regurgitation since childhood. In addition aortic root dilatation was documented over six years by means of echocardiography and had been followed up regularly in a district hospital. Echocardiography six months before pregnancy had shown minimal mitral and aortic regurgitation and aortic root dilatation of 4.1 cm; left ventricular function was normal. Repeat echocardiography evaluations during pregnancy confirmed an aortic root dilatation. Routine booking and screening investigations were all within normal limits. At the 25th week, admission was necessary following a vaginal bleeding, without pain contraction. Echography showed a placenta praevia and cervical dilatation 2.8 cm of diameter. Bed rest and intravenous thocolitic therapy were immediately enhanced. A cervical cerclage, as described by McDonald, was placed. At the 37th week the patient was admitted and cerclage removed before the caesarean section. A healthy female of 2900 g was born. The postoperative period was favourable and patient was discharge after 7 days. In the present case, it is suggested that cervical incompetence and placenta praevia may be caused by an alteration of microfibrillar fibers.