We present a case of untreated type II odontoid fracture, which evolved in severe dislocation 18 months later. Delayed dislocations in untreated type II odontoid fractures are already reported in literature. The singularity of our case is that CT-scan showed signs of fusion in the right C1-C2 articulation, which could have required a more complex surgical procedure to realign the upper cervical spine. Surprisingly, a CT scan performed in the extension position showed complete mobility of C1 and allowed us to perform a one stage posterior fixation. We want to highline both the importance of treating an Anderson type II fracture to prevent dislocation (acute or delayed), and the possibility to perform a flexion-extension CT scan to project a better surgical plan.