Secondary hydrocephalus communicans after traumatic upper cervical spine injuries with leakage of cerebrospinal fluid is a rare and hardly described complication. A case of a 75-year-old woman sustained a type II dens axis without other injuries, especially without evidence of a hydrocephalus in the primary CT scan. Dorsal atlanto-axial fusion was performed. Postoperative drainage was prolonged and positive for β2-transferrin. Wound revision with an attempt to seal the leakage was not successful. Secondary CT scans of the brain were performed due to neurological deterioration and showed a hydrocephalus with typical EEG findings. No anatomical reason for a circulative obstruction was found in the CT scan. After application of a ventriculo-peritoneal shunt the neurological status improved and the patient could be discharged to neurological rehabilitation.