One hundred consecutive patients with displaced fractures of the tibial shaft were randomly assigned to two groups, one treated with AO-plate fixation and the other with conservative methods. Strictly conservative treatment failed in two patients because of the interposition of muscles. Comparison of the groups showed that a longer duration of hospital stay was needed in the AO-plate group, and there were also more complications in that group. However, the median healing time was shorter and the anatomical end results were better than in the conservatively treated patients. Closed longitudinal fractures were found to be suitable and open fractures, unsuitable for AO-plate fixation. In the group that was treated conservatively most fractures that healed in malalignment were located in the distal third of the tibial shaft.