The early identification of the Marfan Syndrome should be essential for the prevention of the aortic dilatation and dissection, but the wide phenotypic expression of the disorder makes the clinical diagnosis very difficult. The aim of this study is to emphasise the necessity of a widely applicable method of morpho-clinical diagnosis. The diagnosis was confirmed on surgical biopsies from ascending aortic wall and aortic cusps, using routine morphological techniques. The macroscopical examination revealed a thin ascending aortic wall, presenting a transversal intimal tear, without secondary dissecting hematoma, and an aortic dilated annulus, producing aortic regurgitation. Microscopically, the diagnosis was supported by the identification of cystic medical necrosis, a specific degenerative lesion in the Marfan Syndrome, in patients with or without family history of aortic aneurysms. This study defines the morpho-clinical changes of the disease, emphasising the necessity of a permanent monitorization of the patient after surgery, due to the risk of late complications.