At present the newer computerized tomography scanners provide a means for direct measurement of the size of normal and abnormal body structures from monitor. In orthopedics and rheumatology, CT is very important and useful means to make correct diagnosis and treatment modalities. In spite of its increasing importance in orthopedic field, reports about accuracy of CT are not common. We reviewed several reports that described about anatomical measurement using CT or similar experiments to our study. But there are few statements that have directly compared CT and caliper measurements in spine or other bones. So, authors performed experiments with 36 vertebrae of 8 pig spines to know the difference of CT measurement from actual measurement. The results were as follow: 1. In CT, bony portions including diameter of body and both pedicles were overestimated about 5% than actual ones. 2. In CT, AP and lateral diameters of spinal canal were 6~7% smaller than actual measurement and canal area, estimated by the products of AP and lateral diameter of spinal canal, is about 13% smaller than actual size. 3. It is the result of cortical overestimation around canal that spinal canal area was estimated less than actual size. 4. Main cause of this differences was partial volume effect that developed during CT scanning. In conclusion, CT scanner is the useful means and gives many useful informations to diagnose the spinal disease, but the physicians must understand mechanical, physical and mathematical limitations of CT and discrepancy of measurement data.