The axes of the kidneys in children with a thoracolumbar gibbus deformity may be distorted to simulate a horseshoe kidney. Measurements of the angle of the gibbus and the angle of intersection of the renal axes were made in 68 children with thoracolumbar meningomyelocele. Thirty-eight children with a gibbus deformity and thoracolumbar meningomyelocele had an abnormality of the renal axis on supine urography, including 19 (28 per cent) in whom a horseshoe kidney was suggested. Three additional children with a gibbus deformity and thoracolumbar meningomyelocele had a normal renal axis. Regression analysis of these data indicated a linear relationship between the angle of the gibbus and the amount of deviation of the renal axis for the values studied. Nuclear scintigraphy, ultrasound studies and clinical records were reviewed in all 41 children with a gibbus deformity. In none were the kidneys fused. There were 21 children with thoracolumbar myelomeningocele who had no gibbus deformity and a normal renal axis. Six other children will be described in detail, 2 of whom were excluded because of severe scoliosis and 4 with congenital renal anomalies.