The aetiology of adolescent idiopathic scoliosis (AIS) remains an enigma. In the literature there are two opinions: one believes a deviating growth pattern is responsible for the condition – patients with AIS tend to be growing faster/be taller – while the other opinion assumes that the growth pattern is normal, but its presence is necessary to allow the development of the scoliosis. We discuss the two stage hypothesis: the natural history of AIS involves an initial stage in which a small curve develops due to a small defect in the neuromuscular control system and a second stage during adolescent growth in which the scoliotic curve is exacerbated by biomechanical factors.