The Harrington instrumentation system was the first widely used, internationally accepted internal fixation system for the correction of idiopathic scoliosis when combined with a spinal arthrodesis. It has been generally available to the orthopedic surgeon for more than 25 years, and therefore its capabilities and limitations have been identified through this long experience. Its implantation requires minimal invasion of the spinal canal and is associated with a low (less than 0.5 per cent) incidence of neurologic complications. It provides predictable correction of spinal deformity with little subsequent loss of correction. When compared with other newer, more complex internal fixation systems for spinal deformities, the Harrington system has a shorter, less difficult "learning curve"; requires less operating time and blood loss to insert; implants a smaller mass of metal; and in some cases costs substantially less for the implant system. The Harrington system has an extremely low incidence of hook dislodgment and pseudoarthrosis formation in single thoracic curves, being reported as near zero for these curves in two recently published series. Conversely, there are some disadvantages to the Harrington system when compared with other types of fixation. It has limited ability to provide sagittal plane control. It does not effectively and predictably derotate the spine. A recent study showed that at an average of 4 years postoperatively, nearly two thirds of the patients had an actual increase in their rib prominence. The pseudoarthrosis rate is high, up to 4 per cent, in the thoracolumbar and lumbar spine. Hook dislodgment approaches 3 per cent when used below the thoracic region. Another disadvantage is the necessity for postoperative external support. As a result, the Harrington system remains an excellent means of treating single and double thoracic idiopathic curves in a safe and predictable manner, while admittedly having limited derotation and sagittal plane control. Other systems that are more sophisticated at segmental fixation of the spine appear to be more appropriate for scoliotic deformities requiring fusion of the thoracolumbar or lumbar spine and those associated with significant sagittal plane deformities.