Aim:The objective of this study is to compare the accuracy of determining pathologic segment between three-position MRI (3P-MRI) and PMCT (post-myelographic CT) in in CSM by assessing the degree of inter-observer and intra-observer agreement. Material and Methods:We retrospectively reviewed 3P-MRI and PMCT of 136 patients who underwent operation for the diagnosis of multi-level CSM. Using an assessment scale, 8 blind observers with various clinical experiences examined 5 parameters: spinal canal narrowing, foraminal stenosis, bony abnormality, intervertebral disk herniation, and nerve root compression. Spinal canal, neural foraminal, spinal cord and disc protrusion diameters were measured. Intra-observer and inter-observer agreement of each images were analyzed. Results:Spinal canal width and foraminal diameter was found to be significantly smaller in 3P-MRI compared to PMCT. No significant differences of cervical cord diameter and the size of disc protrusion measured in 3P-MRI compared to PMCT were observed. Comparing between 3P-MRI and PMCT, disc abnormality and nerve root compression showed better agreement on 3P-MRI, whereas foraminal stenosis and bony lesion showed better agreement on PMCT.Conclusion:In the present study, PMCT was still useful in diagnosis of the foraminal stenosis and bony lesion compared to 3P-MRI but showed limitation in disc abnormality and nerve root compression. Even though PMCT may provide valuable additional information in difficult or ambiguous cases, universal standard of 3P-MRI proved higher reliability in detecting pathologic levels in the CSM patients.