The medical records and radiographs of forty-two adolescents (twenty-three male and nineteen female) who had had a posterolateral spinal arthrodesis for spondylolisthesis between 1950 and 1986 were reviewed to assess the long-term outcome of this form of treatment. The average age of the patients at the time of the operation was fourteen years (range, seven years and nine months to seventeen years and eleven months). The duration of the clinical and radiographic follow-up ranged from two years to twenty-seven years and seven months. All patients had an in situ arthrodesis of the involved vertebrae. Eighteen patients had no additional intervention, and twenty-four patients had reduction and application of a cast. Use of the cast led to a decrease in sagittal translation of more than 5 per cent in eighteen patients and a decrease in lumbosacral kyphosis (the slip angle) of more than 5 degrees in fourteen patients. Of the patients who did not have a cast, eight had an increase in sagittal translation of more than 5 per cent and ten had an increase in lumbosacral kyphosis of more than 5 degrees. There were no neurological problems at the time of the initial operation or after the reduction maneuver. At the most recent clinical follow-up examination, thirty-eight patients had no complaints of low-back pain or any restriction of work-related or recreational activities. Persistent low-back pain and pain in the lower extremities limited the activities of the remaining four patients, two of whom had another operation to alleviate these symptoms.