This study was undertaken to ascertain whether repair and/or reconstruction of the scapholunate interosseous ligament can prevent or reduce the occurrence of carpal instability and improve the clinical results. Thirty-two patients with lunate and perilunate dislocations were treated in the last 12 years. Of the 32, only 2 patients were seen within 4 weeks of injury, and the remaining 30 patients were seen and treated more than 4 weeks after the dislocation. Patients were followed for an average of 5 years. The scapholunate interosseous ligament was repaired and reconstructed in 12 patients (group 1). In 20 patients the ligament was not repaired or reconstructed (group 2). Clinical results were expressed by a modification of the point score method of Green and O'Brien. The scapholunate angles were measured on the lateral x-ray films with the wrist in neutral position. In group 1 clinical results averaged 82 points, while in group 2 they averaged 59 points. The scapholunate angles in group 1 averaged 50 degrees whereas in group 2 they averaged 69 degrees. These clinical and x-ray film results suggest that scapholunate interosseous ligament repair and/or reconstruction can prevent or reduce the occurrence of carpal instability and improve clinical results.