Scoliosis: Lateral (sideways) curving of the spine. The degree of scoliosis may range from mild to severe. Of every 1,000 children, 3 to 5 develop spinal curvature that is considered severe enough to need treatment. Adolescent idiopathic (of unknown cause) scoliosis is the most common type and appears after the age of 10, commonly in teens. Girls are more likely than boys to have this type of scoliosis. Scoliosis can run in families, so a child who has a parent, brother, or sister with idiopathic scoliosis should be checked regularly for this condition. Severe scoliosis may require treatment that includes bracing, casting, surgical correction, and/or physical therapy.