Study Design. This is a prospective case-control study.Objective. The objective of this study was to compare 3D morphologic parameters of the spine at the first visit between a non progressive (NP) and a progressive (P) group of immature adolescent idiopathic scoliosis (AIS).Summary of Background Data. Prediction of curve progression remains challenging in AIS at the first visit. Prediction of progression is based on curve type, curve magnitude and skeletal or chronological age.Methods. A prospective cohort of 134 AIS was followed from skeletal immaturity to maturity (mean 37 months). The first group was made up of AIS patients with a minimum 6° progression of the major curve between the first and last follow up (P) (n=53) and the second group was composed of NP patients that reached maturity with less than 6° progression (n=81). Computerized measurements were undertaken on reconstructed 3D spine radiographs of the first visit. There were 6 categories of measurements: angle of plane of maximum curvature, Cobb angles (kyphosis, lordosis), 3D wedging (apical vertebra, apical disks), rotation (upper and lower junctional vertebra, apical vertebra, thoracolumbar junction), torsion and slenderness (height/width ratio). t tests were also undertaken.Results. There was no statistical difference between the two groups for age and initial Cobb angle. NP presented significant hypokyphosis, and parameters related to rotation presented significant statistical differences between NP and P (plane of maximal curvature, torsion, apical axial rotation). Depth slenderness also presented statistical differences.Conclusion. This study confirms that even at the initial visit, 3D morphologic differences exist between P and NP AIS. It supports the use of 3D reconstructions of the spine in the initial evaluation of AIS to help predict outcome.