Pedicular screw fixation has many advantages, such as, achievement of rigid fixation through the pedicle which is the strongest part of spine, almost perfect anatomic reduction by direct force on the deformed sites, and preservation of the mobile segements by short segment fixation. This modality, however, also has some inherent risk because accurate insertion of pedicular screw is sometimes difficult and troublesome. and therfore, there is a chance of neurologic injury due to the anatomic correlation between pedicle and nerve root. The authors assessed the placement of the 224 pedicular screws by measuring plain film image and by its geometric calculations of the measurement in 55 patients treated by AO “Fixateur Interne” during the period of 28 months from April 1988 to July 1990 and following results were obtained; l. Age of the cases ranging from 16 to 69, majority were women over 40 years-old. 2. The subject of the study consists of 20 spondylolisthesis, 15 spinal stenosis, 13 spine fracture, 4 H.N.P. with instability and 3 kypho-scoliosis cases. 3. The anatomic pedicles diameter on transverse and sagittal plane is wider than the 6mm, It is fairly larger than the Schanz scerw diameter, 5mm, and so, a little discrepancy in the insertion angle is permitted. 4. There was one case of neurologic damage, in this case, there was no difference concerning the insertion angle, the neurologic damage arose due to the point of entry which was sligltly medial. 5. C-T scan is required for post operative evaluation but due to high cost and metallic artifact, the authors used plain X-ray as evaluation mode.