A case of annulo‐aortic ectasia was reported. The patient was a 44 year old Japanese female who expired shortly after the operative intervention against aortic aneurysm and aortic insufficiency. This is the first case of annulo‐aortic ectasia reported in Japan.Histological findings of the resected aneurysm revealed pronounced cystic medial necrosis. At autopsy, similar medial necrosis was found in the remaining aorta, pulmonary artery and some of the major branches of the aorta. The aortic valve cusps also showed myxomatous accumulation of acid mucopolysaccharides and hypoplasia of annular connective tissue. The aortic ring was dilated with evidence of regurgitation.Problems related to pathologic findings were discussed with special reference to a forme fruste manifestation of Marfan's syndrome. We believe cases, such as presented here, should not be considered as a forme fruste of Marfan's syndrome with the present knowledge of the disease, in spite of the morphologic similarity of lesions in our case with those described in classical Marfan's syndr