Cardiovascular manifestations of Lobstein's disease are rare, probably unrecognized, and determining factors for the final prognosis, the most frequent lesion being aortic incompetence. The eleventh case to be reported with pathological findings in the literature is described. This complication is usually found in men, blood regurgitation being large in amount, symptomatic, and progressive. Its mechanism is related less to dilatation of the aorta and its ring than to valvular changes, they being frequently bicuspid and dysplasic. Histological findings, not however pathognomonic, are myxoid degeneration in the valves and parietal cystic necrosis in the aortic wall. Apart from the absence of an aneurysm and aortic dissection, macro- and microscopic lesions are similar to those observed in Marfan's syndrome and osteogenesis imperfecta. Operative therapy was employed in all eleven cases, with three postoperative deaths and three later deaths. Certain complications arise from uncontrollable severe hemorrhage, which justifies the use of valve heterografts not requiring antivitamin K administration.