The case of a 62-year-old patient with an atlanto-axial synovial cyst is presented. The narrowing of the spinal canal was associated with anterior medullar compression and neurological deficit. A transoral approach with odontoid resection was performed. The diagnostic of synovial cyst was histologically confirmed. Secondary atlanto-axial instability required posterior fixation completed by C1-C2 transarticular screw fixation. The follow-up showed an improvement of the neurological deficit. Similar cases reported in the literature are reviewed and discussed.