Background: Low back pain (LBP) is a very common musculoskeletal disorder. Lumbar range of motion (ROM) and posture are parameters which are commonly assessed in LBP research. Reliable methods of measuring lumbar spine ROM and posture are needed. The CODA motion analysis system has several potential advantages over other motion analysis systems; however its reliability for lumbar spine analysis has not been examined. This study investigated the reliability of the CODA system for measuring lumbar spine sagittal plane ROM and posture. Methods: Twelve participants were tested by two investigators on two occasions. Ten trials of lumbar ROM and usual sitting posture were performed. The reliability of upper lumbar, lower lumbar, and pelvic sagittal plane motion was assessed using intra-class correlation coefficients (ICC) and Bland and Altman methods, including evaluation of the mean difference and limits of agreement. Results: Levels of association were very good for ROM, for both intra-rater and inter-rater measurements (all ICC >0.7). However, agreement was more variable, with some lower lumbar and pelvic regions displaying large mean differences and wide limits of agreement. Overall, greater reliability was obtained for the upper lumbar region angles, and for intra-rater comparisons. Conclusion: Reliability of the CODA system varied from very good to fair, depending on the parameters assessed. While good association was found between most parameters, the level of agreement was only fair to moderate. Recommendations are made to improve the protocol used to assess spinal motion, which may improve reliability. © 2010 - IOS Press and the authors. All rights reserved.