METHODS A retrospective study. OBJECTIVE We assessed risk factors for lumbosacral plexus palsy related to pelvic fracture that can be evaluated during the acute injury phase with diagnostics such as computed tomography (CT). BACKGROUND Many patients with pelvic fracture are in vital shock, with polytrauma and loss of consciousness, making an accurate neurologic examination very difficult in the emergency room. METHODS This study included 22 patients who had AO classification type B or C pelvic fractures. The 22 patients had 27 posterior osteoligamentary lesions. The average injury severity score (ISS) was 27.5 (range, 16-50). Age, sex, ISS, suicidal jump, longitudinal displacement, sacral transverse fracture, pubic fracture, lumbar transverse process fracture, type of pelvic fracture (AO), and type of sacral fracture (Denis) were examined for a correlation with the lumbosacral plexus palsy. Using coronal reconstruction CT, we considered a 10 mm or greater displacement at the sacrum or sacroiliac joint to be a longitudinal displacement. Transverse sacral fracture was diagnosed by sagittal reconstruction CT. RESULTS Of the 22 patients, 5 (22.7%) had lumbosacral plexus palsy (8 of 27 pelvic fractures) detected during treatment. The incidence of lumbosacral plexus palsy was not related to age, sex, ISS. Incidence of palsy was significantly higher when the patient's affected side had longitudinal displacement. Patients who had made a suicidal jump or had a sacral transverse fracture also had a significantly higher risk for lumbosacral plexus palsy. Palsy was not related to the type of pelvic fracture (AO) or sacral fracture (Denis). CONCLUSIONS In this study, longitudinal displacement of the pelvis, transverse sacral fracture, and trauma from a suicidal jump were risk factors for lumbosacral plexus palsy. These risk factors were helpful in our examination of patients who had severe pelvic fracture with loss of consciousness.