Cosmesis is important in the treatment of adolescent idiopathic scoliosis patients. The aim of this study was to quantify the cosmetic defect using parameters of the ISIS (Oxford Metrics Ltd. Oxford, England) scan. Ten nonmedical judges scored photographs of 100 adolescent idiopathic scoliosis patients based on cosmetic criteria. This Cosmetic Spinal Score proved to be a reliable figure. The Cosmetic Spinal Score was then compared with ISIS parameters and the Cobb angle. An equation based on ISIS parameters was developed, which could predict Cosmetic Spinal Score with sufficient reproducibility to have a useful clinical application. Bracing reduced the rib hump but not enough to improve the cosmetic appearance. Spinal fusion and Harrington instrumentation improved all measured parameters influecing physical appearance.