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Purpose To determine the normal values of the anterior atlantodental interval (AADI) and posterior atlantodental interval (PADI) on plain radiography, multidetector CT (MDCT) and MRI, as well as the dural sac width and spinal cord diameter at the atlantoaxial joint level on MRI. Materials and Methods In total, 60 subjects underwent plain radiography, MRI and MDCT. We obtained values for AADI and PADI on plain radiography, MDCT, and MRI, and for dural sac width and spinal cord diameter on MRI. Two radiologists independently measured each value and a consensus was reached. Results The average AADI was 1.5 ± 0.5 mm on plain radiography, 1.4 ± 0.3 mm on MDCT, and 1.6 ± 0.5 mm on MRI. The average PADI was 20.6 ± 2.4 mm on plain radiography, 18.0 ± 2.1 mm on MDCT, and 17.7 ± 1.9 mm on MRI. The dural sac width was 13.7 ± 1.8 mm, and the spinal cord diameter was 7.8 ± 0.7 mm. Interobserver agreement was 0.701-0.927 and intraobserver agreement was 0.681-0.937. Conclusion AADI values obtained on MDCT are significantly lower than those obtained on plain radiography or MRI. PADI values obtained on plain radiography are significantly higher than those obtained on MDCT or MRI. The dural sac width is most closely correlated with PADI values on MDCT. PADI seems to be easier to measure, more relevant, and clinically useful than AADI.