What is scoliosis? Scoliosis is a disorder in which there is a sideways curve of the spine. Curves are often S-shaped or C-shaped. In most people, there is no known cause for this curve. Curves frequently follow patterns that have been studied in previous patients (see "Curved patterns of the spine" diagram). People with milder curves may only need to visit their doctor for regular check-ups. Some people who have scoliosis need treatment.