The purposes of this study were to identify lumbar lordosis in low back pain patients and to investigate differences in lumbar lordosis in low back pain patients according to etiologies. On the basis of the findings of spinal roentgenogram, MRI, and SPECT imagies, the patients were divided into four groups; 1) facet syndrome with facet joint inflammation or degenerative change, 2) disc herniation including disc bulging or extrusion, 3) combined low back pain accompaning facet joint lesion with disc herniation, 4) simple low back pain with no abnormal imaging findings. There were statistically significant decrease in low back pain patients compared with normal controls in terms of lumbosacral curvature. No sex and age differences were observed within low back pain patients and normal controls in terms of lumbosacral curvature. The review disclosed a significant decrease of the lumbosacral angle in order of simple low back pain, disc herniation, combined low back pain compared with normal controls. But facet syndrome patients showed no change of lumbosacral angle. Patients with disc bulging showed no significant decrease of lumbosacral angle compared with normal controls but patients with disc extrusion showed significant decrease. It is believed that the decrease of lumbosacral angle in low back patients results from a pathokinesiological effort to keep facet joint from pressure stemed from facet overlying and to minimize the shearing force over lumbosacral joint. The facet joint stiffness due to inflammation may play a major role in no change of lumbosacral angle in facet syndrome patients. In conclusion, different causes of low back pain should be taken into consideration for the assessment of lumbosacral angle.