Thirty-two adolescent girls braced for late onset idiopathic scoliosis at Children's Hospital, Boston were compared with thirty-two untreated girls from Our Lady's Hospital for Sick Children, Dublin, Ireland paired on the basis of curve size and site and age at diagnosis. All were Risser 0 at diagnosis. Study period for the braced group was from brace initiation to part-time brace wearing and, for the controls, from diagnosis to last review. There was no statistically significant difference between the groups on any parameter of curve progression. This study raises questions about the efficacy of spinal orthoses in modifying the natural history of late-onset idiopathic scoliosis and removes the ethical problems inherent in a prospective trial in which the only treatment permitted to the control group is surgery.