This paper presents a comparison of 4 different methods used to describe the “plane of maximum deformity” of scoliotic spines. It was conducted on 31 scoliotic subjects with a right thoracic curve. Most techniques are reproducible and are little influenced by reconstruction errors. The measurement of the plane of maximum deformity gives quite different orientations and there is not a “best technique”, even if most of them are correlated. The spinal curves presented different shape patterns, which may explain the discrepancy in the results between the methods. We recommend using the segment between the end vertebrae to calculate the plane of maximum deformity, and being careful when comparing published results using these techniques because they are not equivalent, even if correlated.