A 42-year-old woman with the diagnosis of aortic regurgitation was admitted to hospital for surgical treatment. Ten years ago, primary antiphospholipid syndrome had been diagnosed, and she had a history of recurrent spontaneous abortions and deep vein thrombosis. She was suffering from moderate exertional dyspnea and chest pain. Catheter investigation revealed progressive dilatation of the left ventricle and a deterioration of the ejection fraction. The aortic valve was excised and replaced with a mechanical valve. A specimen of the aortic valve showed localized thickening and shrinkage of the midportion and base of each cusp, with vegetation on the surface. These localized, specific findings suggest that another mechanism may be involved in the cardiac valve pathology in patients with primary antiphospholipid syndrome. No hemostatic or thromboembolic problems were encountered after the surgery, and her postoperative course was uneventful.