The article describes the biomechanical aetiology of the so-called idiopathic scoliosis (1995 – 2007), known as an adolescent idiopathic scoliosis (AIS). The first lecture dealing with the issue was delivered in Hungary in 1995. The first publication was made in Germany in 1996 (Orthopädische Praxis). Biomechanical development of scoliosis. The scoliosis appears as the secondary deformity originating in the asymmetry of hips’ position and movement described by Prof. Hans Mau in articles about Syndrome of Contractures (Fig. 1, 2a, 2b, 3, 4a, 4b, 4c). Next - while walking and while standing ‘at ease’ on the right leg (T. Karski). The research proves that the right leg is the preferred one over the years for standing. This phenomenon is because of better stability of right leg in region of right hip during standing and this is because of smaller adduction in straight position of joint. Every type of scoliosis starts to develop at the time when the child starts to stand and walk. Depending of types of scoliosis is a special characterise of patho-morphology of deformity of spine and their various properties. To explain in details the biomechanical aetiology we must remember about the three asymmetries causing the development of scoliosis: