Two comparable groups with unstable thoracolumbar fractures have been studied: one consisting of 23 patients treated conservatively and one consisting of 20 patients treated surgically with Harrington instrumentation. The vertebral injuries have been analysed radiologically at the time of injury as well as after completion of conservative and surgical treatment and at follow-up on average 6 years and 3 months after injury in the conservatively treated group and 2 years and 2 months after injury in the operated group. The vertebral fractures were often solitary at the L1 level with a characteristic radiologic appearance and mainly caused by flexion-rotation injuries. There were indirect signs of associated ligament injuries in most cases. Indirect signs of associated disc injury were found in 77 per cent of the cases, most of them related to the superior disc. The signs of disc injury were accentuated at the two follow-up examinations. In the operated group, the radiologic appearance of the vertebral body normalised after Harrington instrumentation. A preoperative gibbus angle of 19.4 degrees was reduced to 6.8 degrees on average postoperatively. In 13 of the operated cases the rods were removed. Among these patients the gibbus angle increased to 17.6 degrees at the final follow-up examination, compared with 11.9 degrees in the patients who had their rods retained. This difference in gibbus angle was significant. In the conservatively treated group, the initial gibbus angle of 19.5 degrees continuously increased to 27.6 degrees at the follow-up examination. All vertebral fractures had healed at the follow-up examination.