Surface topography (ST) is a tool used to assess adolescent idiopathic scoliosis (AIS), which affects females more severely than males. However, current ST techniques fail to measure breast asymmetry related to torso deformity. Cosmetic deformity is important to patients because poor body appearance can cause psychological distress. Breast asymmetry is especially important to adolescent females. This study develops a method for assessing breast asymmetry using ST in patients with AIS, and proposes a reliable breast asymmetry classification for such patients. To achieve this, ST torso scans of 25 females (age: 15.4 ± 1.3 years; range: 13.5 - 17.5 years) with AIS were obtained. Scans were analyzed using a method that finds a rotoinversion matrix to minimize the distance between the torso scan and its reflected image about the sagittal plane. The mirrored torso was then fitted to the original torso using an iterative least- squares method, such that the average deviation between the observed and reflected torsos was minimized. The relative deviation between the two torsos was measured and displayed as a deviation colour map (DCM). Each patient’s DCM was visually appraised by two of the authors and a breast asymmetry classification system was created based on this appraisal. Good intra- and inter-rater reliability was found for the classification decisions by five observers. All of the patients presented breast asymmetry that could be reliably categorized into the proposed five-group classification with all patients exhibiting deviations exceeding the threshold of 3 mm between sides routinely observed in healthy teenagers without scoliosis.