The reliability of assessing facet joint obliquity from standard CT scans in the lumbar spine was studied. There was no significant difference in repeated measurements by one single examiner, nor in measurements made by different examiners. Measurement of facet joint obliquity from CT scans made on different occasions was not significantly different either. This reproducibility occurred despite the fact that adjacent CT scans from one joint extremity to the other showed variation in obliquity of about 11%.