The article examines the biomechanical etiology of so-called idiopathic scoliosis (AIS). It describes I-st, II-nd and III-rd etiopathological groups (epg) of spine deformity which were developed during the years 2001/2004/2005. All children with so-called idiopathic scoliosis had an abduction contracture of the right hip, often connected with a flexion and external rotation contracture. In other cases we found only limited range of adduction of the right hip in comparison to the left hip. We maintain that children with this real abduction contracture of the right hip constitute the first etiopathological group of the development of scoliosis (I-st epg). This group has an “S” double shaped scoliosis with the rib hump on the right. Other patients, with only limited adduction of right hip in comparison to the left hip, constitute the second etiopathological group of development of scoliosis (II-nd epg). This group has a “C” shaped lumbar, sacro-lumbar or lumbo-thoracic left convex scoliosis. The third etiopathological group (III-rd epg) shows either no or a minimal curve on X-ray with either no rib hump or a very minor one but have a “stiffness of spine”. Such patients have problems with sporting activities and, as adults, the spinal stiffness leads to considerable “back pain”. The right hip structural abduction contracture, or the differences in adduction, is connected with the “syndrome of contractures” in neonates and babies described by many authors and in depth by Mau. How does scoliosis develop? Our explanation is as follows. Asymmetry of movement of the hips during gait provokes asymmetry of loading and asymmetry of growth of both sides – left and right – and the gradual development of scoliosis. In I-st epg, the scoliosis is a secondary compensation for deformities in the pelvis and spine. The II-nd epg is linked to a permanent standing posture maintained on a free right leg during the first years of life. The III-rd epg comprises of patients from the boarder groups of I-st and II-nd epg. This classification establishes a clear therapeutic approach to every etiopathological group of scoliosis and allows for the possibility of introduction of causative prophylaxis.