Adolescent idiopathic scoliosis (AIS) is one of the orthopedic disorders in which clinical evidence of sexual dimorphism is most marked. Sexual dimorphism in spine growth, morphology, stiffness, curve pattern, and hormones may be the environment in which genetic factors combine to produce the phenotype of a scoliosis patient. These factors also may play a role in the curve progression despite treatment and may help explain why some patients' curves never change and others are recalcitrant to nonoperative treatments. There are important differences in male and female AIS that impact diagnosis, treatment, and outcomes.