Fifteen patients with unstable pelvic fractures were treated with immediate anterior external fixation followed by delayed posterior fixation, including five sacroiliac lag screws, six transiliac rods, and four iliac plates. Initial anterior external fixation aided in resuscitation of hemodynamically unstable patients and allowed early mobilization. Delayed posterior internal fixation avoided infection and hemorrhage but failed to achieve anatomic reduction of disrupted sacroiliac joints and sacral fractures. Followup examination confirmed maintenance of fixation and fracture healing but pain and persistent neurologic deficits were common findings. Lumbosacral nerve plexus injuries occurred in patients with fractures through the sacral foramina. Fixation of these fractures with sacroiliac screws and transiliac rods caused overcompression and the resulting foraminal encroachment may be a factor in the lack of neurologic recovery. In this study, delayed posterior internal fixation was not associated with perioperative morbidity and achieved better reductions than those obtained with external fixation alone. Delaying the fixation, however, increased the difficulty of obtaining anatomic reduction of certain posterior arch disruptions.