The AO Internal Fixator is the most popular device, nowadays, in the surgical treatment of thoracoiumbar spine fractures. The device consists of long Schanz screws inserted into the vertebral bodies, from a posterior approach, through the pedicles and of connecting threaded longitudinal rods carrying mobile clamps that can be fixed in eve-ry position by nuts. The long iever arms of the Schanz screws provide manual reduction during the operation. since the device is stable against flexion anmd rotatıon by itself, the fixation can be restricted to the most immedi-ate adjacent vertebrae which leaves the rest of the spine mobile. in our clinic the AO Internal Fixator intrumenta-tions have been starkted in May 1989. The early results of these instrumentations have shown that the implant is one of the most reliable methods in the surgical treatment of lower thoracic and lumbar vertebrae fractures. This report presents and discusses 59 instrumentations in fresh fractures. The main advantage of the appiication is the short fixation area and the ease of postoperative treatment.