The most common manifestation of cardiovascular syphilis, a rare diagnosis since the introduction of penicillin, is aortitis of the ascending aorta. Since the majority of patients with uncomplicated aortitis are asymptomatic, early diagnosis is difficult. We report the case of an HIV-positive patient with asymptomatic syphilitic aortitis that was incidentally diagnosed with F-18-fluorodeoxyglucose (FDG) positron emission tomography (PET). We conclude that FDG-PET could become a promising new imaging technique for both diagnosis and follow-up of patients with syphilitic aortitis.