The pathoanatomy and natural history of scoliosis associated with Duchenne muscular dystrophy were established by a review of 105 patients. Scoliosis developed in 95% of these patients after the loss of ambulation. The direction of the curve was determined by asymmetrical contracture of the iliotibial band. Functional classification using the radiographic sitting kyphotic index proved a reliable guide to the age at loss of ambulation and life expectancy, as well as the rate of progression and eventual severity of spinal deformities. Spinal orthoses failed to control curve progression in 94% of patients (30 of 32). Fourteen patients underwent spinal fusion with excellent long-term results.