Understanding the cause of adolescent idiopathic scoliosis is important for elucidating its pathogenesis. Epidemiological investigations have demonstrated that the incidence of idiopathic scoliosis is approximately 2% in patients with a Cobb angle of 20°. The proportion of patients with adolescent idiopathic scoliosis who are need of treatment is only 0.1% to 0.3%. The wide range of curve magnitudes in patients with idiopathic scoliosis suggests the presence of multiple genetic and environmental factors1-3. Various theories have been proposed regarding the cause of idiopathic scoliosis, but none have been widely accepted3. Based on historical and recent findings regarding the cause of idiopathic scoliosis, the present report reviews the muscular theory, neurological theory, connective tissue theory, bone growth mismatch theory, genetic theory, and experimental animal models of this disorder. The most representative and important report on the muscular theory of adolescent idiopathic scoliosis was based on the electromyographic findings of Le Febvre et al.4. That study revealed potential asymmetry of the erector …