The most common form of scoliosis (lateral curvature of the spine) is adolescent idiopathic scoliosis (AIS). The prevalence of AIS is 10-20 individuals per 1,000 population screened. Progressive AIS affects females more frequently than males. Only 1-2 per 1 ,000 individuals have progressive AIS and need brace or surgical treatment. Early screening programs for scoliosis and other spinal deformities are instituted in schools in the fifth to ninth grades to achieve early detection of progressive AIS. If detected early, progressive AIS can in most cases be successfully treated by use of an external spinal brace. More severe scoliosis is successfully treated with surgical instrumentation and spinal fusion. Although much progress has been made in understanding the natural history of AIS, its cause remains unknown.