Vertebral stabilization using transpedicular screw fixation device is widely used in the surgical treatment of degenerative lumber diseases such as spinal stenosis, pseudospondylolisthesis, and spinal instability. The use of transpedicular screw fixation devices provides substantial advantages with regard to an increase of the rate of solid arthrodesis, early rehabilitation, short segment spinal fusion, and restoration of sagittal lumbar lordosis. The authors analyzed 11 patients showing definite postoperative loss of the lumbar sagittal lordosis in a total of 110 surgical cases of degenerative lumbar diseases who underwent segmental spinal fusion using transpedicular screws from January 1981 to December 1993. The purpose of this study was to analyze the causes of loss of lumbar sagittal lordosis in the instrumented segments and to present some precautions in transpedicular screw fixation for surgical patients with degenerative lumbar spines to maintain corrected lumbar sagittal lordosis. The results from this study were as follows: 1. By standard Cobb lateral measurements, eleven cases in a total of 110 patients showed definite loss of lumbar sagittal lordosis more than 4 degrees. 2. The period reflecting loss of lordosis was roughly within postoperative four months which were critical fusion time of the grafted bone mass, which lasted an average of 4.8 months in this study. 3. The implants led to loss of lordosis consisted of 6 cases in 53 Diapasons, 4 cases in 32 Wiltses, and a case in 15 Steffee plate systems. Diapason & Steffee plate systems were classified as a rigid type and Wiltse system as a flexible one. 4. The causes of postoperative loss of lordosis were recognized as 2 cases of screw toggling, 5 cases of screw-rod locking failure and 4 cases of rod bending. 5. The group resulted in more loss of lordosis in degrees was related to significant change between preoperative and postoperative lordosis, distraction of disc space during operation, extensive discectomy, and reduction of degenerative spondylolisthesis which were the cases of the anterior column deficiency.