The incidence of tertiary syphilis has declined in recent years owing to the early recognition of the disease and use of antibiotics. As a result, syphilitic aortic aneurysms are rarely encountered nowadays. We report the case of a 65 years old man, who was admitted to our hospital in June 2004 for dyspnea, cough and chest discomfort. On physical examination, blood pressure was 130/80 mmHg with no significant laterality, pulse rate was 70 per minute and there was a decrease of breath sounds over the right lung. Laboratory findings revealed a slight elevation of the erythrocyte sedimentation rate. Serological studies for syphilis showed a positive venereal disease laboratory test (VDRL) at 1/32 and a positive Treponema pallidum hemagglutination test (TPHA) at 1/2560. The chest radiography showed a right para cardiac opacity measuring 16 x 12 cm. Fiber optic bronchoscopy showed an extrinsic compression of the right upper lobar bronchus. Gadolinium-enhanced magnetic resonance angiography and 16 multidetector-row spiral computed aortography showed a huge partially thrombosed saccular aneurysm of the ascending aorta measuring 132 mm in diameter. The circulating lumen measured 53 mm in its largest diameter. This aneurysm involved the innominate artery. There was no other arterial involvement. The patient was given a three week course of intravenous penicillin followed by a successful surgical procedure in September 2004 with ascending aortic replacement and innominate artery reimplantation. This case illustrates well a formerly common, but now extremely rare disease.