Introduction: Variation in posterior arch of atlas are very rare. Variation is due to developmental anomaly, its detection is icidentaly while investigation for head and neck region. Our aim is determine the variation in posterior arch of atlas. Materials and methods: 50 dried atlases of unknown sex used for the study from department of Anatomy of medical college of Gujarat. Results and observation: 3 atlases showed absence of median part of posterior arch out of 50 vertebrae. Conclusion: Such variations must be noted by surgeons and radiologist.