Tehran University of Medical Sciences Case Reports in Clinical Practice 2538-2683 2 4 2018 05 14 98 102 EN Mahmoud Khodabandeh Department of Pediatrics, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Katayoun Borhani Department of Urology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Hamid Eshaghi Department of Urology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Mohsen Mohammadi Non-Communicable Pediatric Diseases Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, Iran. Elmira Khodabakhsh Department of Surgery, School of Medicine, Mazandaran University of Medical Sciences, Sari, Iran. 2017 10 30 2018 01 30 Neurosyphilis is defined as central nervous system involvement by treponema pallidum bacteria. Symptomatic neurosyphilis can be manifested as acute or subacute meningitis (a type of meningitis) that emulates other bacterial infections. Hydrocephalus and cranial nerve paralysis (VII and IX) may occur. In this article, we report a case of congenital hydrocephalus neurosyphilis, with a significant improvement in neurological condition after treatment with penicillin-G. The infant was a 2.5-month-old boy who referred to the emergency department because of fever. On initial examination, the head had been larger than usual. The patient was evaluated with suspicion of sepsis. Cerebrospinal fluid (CSF) analysis was consistent with meningitis and hydrocephalus found in ultrasound. Due to lack of response to antibiotic and anti-tuberculosis (TB) treatments in improvement of CSF analysis, ultimately after positive CSF serology in favor of syphilis, treatment changed into penicillin; then clinical and laboratory findings were improved. The rare manifestation of congenital syphilis as hydrocephalus and the appropriate treatment response to penicillin were interesting points for the introduction of this patient. We presented a case of neurosyphilis, which was characterized by a cognitive and neurological deficits, hydrocephaly, and myoclonus, as well as irritability and hearing loss. Since syphilis is easily diagnosed and treatable, it should be considered and evaluated in patients with cognitive defects and motor disorders. Misdiagnosis of syphilis is a serious medical mistake that may cause long-term consequences. https://crcp.tums.ac.ir/index.php/crcp/article/view/148 https://crcp.tums.ac.ir/index.php/crcp/article/download/148/96