The investigators report the case of a 44-year-old man who presented acutely and was found to have saccular aneurysm of the innominate artery, narrowed or totally occluded aortic arch arteries, and marked thickening of the thoracic aorta except for the wall behind the sinuses of Valsalva. The abdominal aorta was entirely normal. Results of the serologic test for syphilis were strongly positive. Because cardiovascular syphilis appears to be a disease that affects the vasa vasora and because these channels are limited to the thoracic aorta, the abdominal aorta is uninvolved, as demonstrated so nicely in the patient described in this case report. Because most patients with cardiovascular syphilis are much older than the patient described, it is unusual to see a perfectly normal abdominal aorta, as in the present patient. In conclusion, syphilis producing aneurysm of the innominate artery is unusual but is always associated with syphilitic involvement of the thoracic aorta.