Meningoencephalitis in neonatal congenital syphilis (CS) is a difficult diagnosis because of the limitation of standard cerebrospinal fluid (CSF) tests. This limitation means that new markers in CSF tests are needed to establish whether meningitis is present in presumptive cases of CS. beta2-Microglobulin (beta2-m) is raised in CSF recovered from neonates with central nervous system (CNS) infections, but it does not correlate with cellular count or proteins in the CSF. We present a preterm newborn with symptomatic CS. First-day CSF showed 50 cells/mm3, protein of 220 mg/dL and a beta2-m concentration of 16.9 mg/dL (normal <2.25 mg/dL). Serial determinations of beta2-m showed a marked reduction (76%) after 10 days of appropriate treatment. At 30 days of life, beta2-m was already within the normal range (1.8 mg/dL). Cerebral ultrasonography showed ventricular dilatation, moderate periventricular echogenicity, subependimal hemorrhages, and linear hyperechoic areas in the thalamus and basal ganglia. We suggest that beta2-microglobulin is very useful in the diagnosis of CNS involvement and in monitoring the response to treatment. In addition, infants with CS may exhibit CNS imaging findings similar to those observed in other intrauterine CNS infections.