Of seventy-four children who were treated at a mean age of seventeen months for neuroblastoma and survived more than five years, fifty-six (76 per cent) had spinal deformity due either to the disease or to the treatment after a mean follow-up of 12.9 years. Of these fifty-six, 50 per cent had post-radiation scoliosis (mean, 18 degrees; range, 5 to 79 degrees), and 16 per cent had post-radiation kyphosis, most frequently at the thoracolumbar junction (mean, 39 degrees; range, 13 to 61 degrees), at the time of follow-up. Two kyphotic thoracolumbar curve patterns were identified: (1) an angular kyphosis with a short radius of curvature and its apex at the twelfth thoracic and first lumbar vertebrae, and (2) a thoracic kyphosis with a long radius of curvature that extended into the lumbar spine. The post-radiation deformity--both the scoliosis and the kyphosis--progressed with growth, the scoliosis at a rate of 1 degree per year and the kyphosis at a rate of 3 degrees per year. Epidural spread of the neuroblastoma was associated with most of the cases of severe scoliosis and kyphosis. The deformity was due either to the laminectomy or to the paraplegia acting in conjunction with the radiation. Eighteen per cent of 419 children with this malignant disease survived more than five years, and of the survivors, 20 per cent had spinal deformity severe enough to warrant treatment. The factors associated with the development of spinal deformity in patient treated for neuroblastoma were: (1) orthovoltage radiation exceeding 3000 rads, (2) asymmetrical radiation of the spine, (3) thoracolumbar kyphosis, and (4) epidural spread of the tumor.