The behaviour pattern of the scoliosis associated with osteoid osteoma or osteoblastoma of the spine is described. In patients presenting with symptoms at or around skeletal maturity, the scoliosis is postural. Excision of the lesion ensures complete resolution of the curve. In the growing child, however, an initial postural scoliosis may develop vertebral rotation with structural characteristics. The magnitude of the curve and the associated vertebral rotation is dependent on the time interval between the onset of symptoms and the surgical treatment. Although removal of the lesion usually results in regression of the curve, a prolonged delay in treatment may result in a progressive structural scoliosis. A possible mechanism for the behaviour of the scoliosis is discussed.