A 74-year-old woman with severe aortic regurgitation and marked thickening of the aortic annulus received aortic valve replacement. Transesophageal echocardiography demonstrated marked thickening of the aortic annulus. The maximum thickness of the aortic annulus was about 11 mm at the side of the right coronary cusp. Histological examination revealed non-specific inflammation of the aortic annulus and aortic valve chiefly composed of lymphocytes and plasma cells. Thickening of the aortic annulus associated with inflammatory aortitis was the cause of aortic regurgitation in this patient.