Twenty-two patients with lumbosacral agenesis were treated at the Shriners Hospital for Crippled Children, Chicago Unit, from 1953 to 1979. At the time of this study, ten of the patients were skeletally mature after an average follow-up of 24.1 years. Two patients had died, twelve could be examined, and eight who were unable to return for examination responded to a questionnaire. Eleven of the patients had diabetic mothers. Of the orthopaedic problems in these patients, knee-flexion contractures with popliteal webbing were the most difficult to correct. These deformities varied in severity with the level of the agenesis and the resulting loss of motor power. Other problems were dislocations and flexions contractures of the hips, scoliosis, equinovarus deformities of the foot, and instability at the spinal-pelvic junction. When there was inadequate quadriceps function it was difficult to correct knee-flexion contractures and to prevent them from recurring. For severe knee deformity, knee disarticulation and prosthetic fitting were the most effective treatment. Spinal-pelvic instability was not a problem in eighteen of the twenty surviving patients. Unreduced dislocated hips also did not cause any problems.