The lumbar facet joints are frequently thought as a source of low back pain. Painful osteoarthritis of the facet joints has been described by many authors. Putti (1927) mentioned "articular tropism" as a causative factor in low back pain and sciatica. Some authorities think that abnormal movement and structural derangement may lead to produce low back pain or intervertebral disc failure with development of CT scanning, as excellent means of studying these joints was introduced. The aim of this study was to CT scan measurements of facet joint orientation by determining intra- and interobserver error of measurement was associated with a number of potential inaccuracies. Thirty cases of healthy young men were examined at department of Orthopaedic Surgery, Yonsei University, Wonju College of Medicine. The results were summerized as follows: 1. The mean and first standard deviation of the facet angle of L4,5 and L6-S1 were 45.9±7.3 and 38.5±9.2. 2. There is not significant intraobserver erro (P >0.05). 3. There is not significant difference of interobserver error at the level of disc space (P >0.05). 4. There is some difference of interobserver error at the level of cartilage end plate and adjacent body on L4,5 & L6-S1 (P <0.05).