Procedures were performed to evaluate the efficacy of using a computer-assisted image-guided system to improve the accuracy of inserting iliosacral screws for posterior pelvic ring injuries. The fluoroscopic method currently in use has shortcomings that do not eliminate the risk to the L5 and sacral nerve roots and iliac vessels. The procedure was performed on embalmed cadaver pelvis specimens with intact soft tissues. Iliosacral screws were inserted across each sacroiliac joint after registering the opposite ilium to simulate a clinical situation. Two trials were performed. The first was necessary to become familiar with the system and test the basic methods of registration. In the second trial, deficiencies were corrected by using spherical-headed fiducial screws for fiducials and a better reference frame clamp, and by better spacing of more fiducials. Results were evaluated by inlet and outlet X-ray views and dissection. All eight S-1 iliosacral 7.0-mm cannulated screws were entirely inside bone. Of the eight S-2 screws, five were inside bone, two infringed upon an S-1 foramen, and one had threads out of the sacral body anteriorly and intruding into an S-1 foramen. This system was felt to be effective and sufficiently safe to warrant clinical trials.