Turner's syndrome is a genetic abnormality which is associated with cardiovascular anomaly in 20% of cases. Coarctation of the aorta and bicuspid aortic valve are the commonest malformations. Aortic dissection is the most serious complication affecting these patients. The authors report the case of chronic aortic dissection of the ascending and transverse aorta in a 27 year old patient with Turner's syndrome. The dissection was diagnosed on angiography. Transthoracic echocardiography showed aneurysmal dilatation of the aortic root. Surgical treatment consisted in replacement of ascending and transverse aorta with a Dacron tube. The anatomopathological analysis showed cystic medianecrosis of the aortic wall. The immediate postoperative evolution was satisfactory. The long-term outcome with a 4 year follow-up was excellent from the clinical and echocardiographic point of view. Turner's syndrome is probably associated with a congenital abnormality of the connective tissue especially of the elastic fibres of the aortic wall, explaining the development, though rare, of aneurysmal dilatation of the ascending and transverse aorta and dissection. These patients should be followed up regularly clinically and by transthoracic echocardiography. Other investigations such as transoesophageal echocardiography, magnetic resonance imaging and angiography are indicated when aortic dilatation, aortic regurgitation or chest pain suggesting aortic dissection are observed.