A 31 year old woman with Marfan's syndrome had a dilatation of the aortic root (55-60 mm at the beginning of pregnancy). Pregnancy was continued with beta-blocker therapy and with regular echocardiographic follow-up. The aortic dilatation increased (62-65 mm) at the last control and, at the 34th week of pregnancy, the patient suffered a dissection of the ascending aorta. A caesarean section was performed with a Bentall procedure during the same operative session. The mother and baby girl are well two years later. The problems of pregnancy in patients with Marfan's syndrome are discussed.