A case of unsuspected classical aortitis with "tree-barking" of the ascending aorta in a young woman with systemic lupus erythematosus and inconclusive syphilitic serologic results is presented. At autopsy, no definite diagnostic clues as to syphilitic or lupic aortitis could be obtained. Although infrequent today, the possibility of complicated cardiovascular syphilis still should be considered. Involvement of the ascending aorta by other systemic diseases is well known and can imitate syphilitic aortitis. Although the possibility of two concomitant diseases cannot be ruled out, the young age of the patient, the weak syphilitic serologic result, and active systemic lupus erythematosus demonstrated in other organs favor a diagnosis of lupic aortitis of the ascending aorta.