1. Syphilitic aortitis is a productive inflammatory process, the earliest and most constant feature of which is a perivascular round cell infiltration in the adventitia. 2. The typical gross picture of luetic aortitis is often obscured by a superimposed, diffuse atherosclerosis. In the early cases the aorta appears fairly normal, presenting only the characteristic histological changes. 3. A pure aortic insufficient valve, with the exception of an infectious endocarditis, is always luetic. 4. Cardiac hypertrophy is not a complication of luetic aortitis. When present it is usually associated with a nephritis. 5. The demonstration of Spirochoeta pallida, even in advanced specimens of syphilitic aortas, is doubtful. 6. An antigen prepared from alcoholic extract of guinea pig heart with the original Wassermann technique should be preferred in diagnosing luetic aortitis. 7. Positive complement fixations in patients suffering with syphilis for a period of about fifteen years or longer suggest the probability, at least, of histological luetic changes in the aorta in 80 to 90 per cent of the cases. 60 per cent of these die from aortitis. 8. About 94 per cent of patients suffering with aortitis give positive Wassermann reactions.