Scoliosis involves spine and trunk deformities. However, during posterior instrumentation of the scoliotic spine, only the exposed spine is currently seen or tracked using navigation systems. A technique for intraoperative tracking of the trunk was developed in order to optimize the surgical correction of the scoliotic trunk deformity. The feasibility of this technique was assessed by comparing the trunk geometry between 19 normal and 21 scoliotic subjects, using an experimental set-up simulating the position adopted during posterior scoliosis surgery. Eleven magnetic sensors placed on anatomical landmarks of the trunk were used to compute nine geometric indices. The geometric indices were closer to zero for normal subjects. Therefore, indices approaching zero during the surgical manoeuvres would indicate a reduction of the trunk asymmetry. Only three of the nine indices were significantly different between normal and scoliotic subjects. This result indicates that the positioning of the subjects on the Relton-Hall frame tends to "normalize" the trunk geometry since the standing position gives more significant differences between normal and scoliotic subjects. The real-time quantification of the trunk geometry during surgical correction of scoliosis may allow the surgeon to improve the correction of both spinal and trunk deformities or to optimize the positioning of the patients on the operating table.