Introduction: Os odontoideum (OO) is a form of odontoid anomaly presented by a separate ossicle with a smooth, sclerotic border not fused with C2 body. The current paper reports a boy with irreducible displaced os odontoideum with severe neurologic deficit after a minor trauma. CasePresentation: A 16-year-old boy admitted in the center due to neck pain and torticollis with neurologic deficit. He had a history of multiple minor traumas. Advanced imaging assessment demonstrated displaced os odontoideum with minimal space available for cord (SAC) and myelomalacia. After unsuccessful closed reduction a 2-stage operation was planned: first, the anterior transoral release and odontoid resection with subsequent halo-traction and second, the posterior atlanto-axial instrumented fusion with bilateral C1 hook and C2 pedicular screws. Conclusions: Congenital anomalies of the odontoid are associated with C1-C2 instability that can be subluxated or dislocated with minor trauma and cause permanent neurologic deficit or even death. When acute cervical spine trauma is imaged, os odontoideum should be distinguished from an acute dens fracture with a multimodality imaging approach including computed tomography (CT), magnetic resonance imaging (MRI) and radiography. Here is the report of a rare case with irreducible displaced os odontiodeum treated him with anterior release, odontoid resection and posterior C1-C2 instrumented fusion.