Of 37 patients with the Prader-Willi syndrome for whom spinal x-rays were available, 32 had a structural scoliosis of 10 degrees or greater. Kyphosis was also found to be more common in older persons with this syndrome, occurring in only one of 14 adolescents but in five of 10 adults. The scoliosis was analyzed in infantile, juvenile, adolescent and adult subgroups. The results suggest that the scoliosis is present from an early age and remains stable during childhood, but progresses in 15 to 20 per cent of cases during adolescence. Scoliosis in patients with Prader-Willi syndrome has many of the clinical characteristics encountered in idiopathic scoliosis. Because it is difficult to detect in these individuals, the authors recommended that baseline spinal X-rays be obtained in all such patients who have suspicious asymmetry of the spine, followed by regular clinical examination, especially during adolescence.