Scoliosis causes complex deformities of the vertebra and rib cage that cascade into deformities of the trunk. The most important feature of scoliosis to those affected is this visible deformity. Instrumentation systems now attempt to improve both internal spinal alignment and external deformity. The deformity includes asymmetrical elevations of the shoulders and hips, prominence of a shoulder blade, a skin fold on the side of the concavity and a subtle twisting of the trunk. The aim of this study was to determine those features that reliably describe cosmetic appearance. Twenty subjects with spinal deformity ranging from none to severe were photographed in a relaxed standing position. Seven blinded evaluators, ranging from a lay person to an orthopaedic spine surgeon, subjectively scored their impression of the trunk appearance, shoulder height difference, shoulder angle asymmetry, decompensation, scapula asymmetry, waist crease, waist asymmetry and pelvic asymmetry. For each criterion, the evaluators placed a mark on a 50 mm line spanning worst to best. The distance to the mark was measured to the nearest millimeter to give a score from 0 to 50. Regression analysis was used with the latter seven features to predict the overall impression. Regression was also used to determine the relative weightings of the features. Although the evaluators gave a subject different scores, there was general agreement in ranking of the subjects (average Spearman’s rho = 0.61). To predict cosmetic impression, five of the seven evaluators chose scapula asymmetry as the best indicator (average r² = 0.58). The next best predictors were shoulder angle asymmetry (r² = 0.43) and waist asymmetry (r² = 0.41). All seven measures of the deformity predicted 85% of the overall impression. Scapula asymmetry, shoulder angle asymmetry and waist asymmetry contribute to 75% of the cosmetic deformity. Objective measures of deformity can be used to evaluate claims that spinal instrumentation improves trunk deformity.