Independent clinical neurological evaluation and intraoperative somatosensory evoked potential (SSEP) monitoring was performed on 30 vertically unstable hemipelvis fractures in 28 patients undergoing acute open reduction and internal fixation. Preoperative ipsilateral neurologic injury of the sciatic/lumbosacral plexus was noted in 15 of 30 fractures (50%). Significant unilateral SSEP changes occurred during manipulative reduction of two displaced sacroiliac joints and one sacral fracture. Because of the expeditious response of the surgical team, with release of traction/retraction, SSEP returned to baseline and no patient sustained an iatrogenic nerve injury or worsening of their preoperatie neurologic status. The incidence of postinjury lumbosacral plexopathy in unstable pelvic fractures is high (50%) when careful preoperative evaluation including SSEP is performed. The use of intraoperative SSEP monitoring is feasible in acute posterior pelvic fracture surgery and can help identify potential intraoperative iatrogenic lumbosacral neurological compromise.