A 37-year-old man was admitted to our hospital for precordial chest pain. He had taken prednisolone (5 mg/day) for systemic lupus erythematosus (SLE) and had been symptom free for the past 12 years. Echocardiography and contrast-enhanced CT of chest showed an enlarged ascending aortic aneurysm, which is rarely seen in SLE. Severe aortic regurgitation was also present, and surgical replacement of the ascending aorta and aortic valve was successfully accomplished by the Bentall procedure. Medial cystic necrosis in the ascending aorta, which is rarely seen in SLE angiopathy, was confirmed by histology. There were no significant histopathological findings in the aortic valve.