BACKGROUND: Neurosyphilis develops into ischemic stroke due to the occlusion of intracranial arteries, which has the histopathological change of intracranial syphilitic arteritis. There might be an association between a latent syphilis and arterial changes before the neurosyphilis develops. We evaluated the relationship between the latent syphilis and the carotid intima-media thickness (IMT) in acute ischemic stroke patients to study whether the latent syphilis affected pathological arterial changes. METHODS: Retrospectively consecutive 96 acute ischemic first ever stroke patients were selected from the Gachon stroke registration from January 2003 to May 2005. The latent syphilis group was made up of 44 patients and the non-syphilis group matched in the age and the sex and consisted of 52 patients. The stroke subtype was classified by TOAST classification. RESULTS: The mean carotid IMT of the latent syphilis group (3.06+/-3.78 mm right, 2.68+/-3.39 mm left) was thicker than that of the non-syphilis group (1.49 +/-2.37 mm right, 1.43+/-1.99 mm left)(p<0.05). The hs-CRP was more elevated in the latent syphilis group than the non-syphilis group (1.6+/-2.2 mg/dl, 1.0+/-2.3 mg/dl respectively) (p<0.05). There were no significant differences of in each of the risk factors between the two groups. CONCLUSIONS: Our results showed the patients with latent syphilis had thicker carotid IMT, and a higher level of hs-CRP than the non-syphilis patients. It could be possible that the latent syphilis attributed to the pathological changes by the inflammation in the extracranial carotid artery.