Four cases of avulsion of lumbar-nerve roots complicating fractures of the pelvis are reported, in which myelographic evidence of diverticula at the roots or dural scarring, or both, were found. In each case, the pelvic injury included dislocation of or fracture adjacent to a sacro-iliac joint. In contrast to fraction injuries of the cervical-nerve roots, the presence of a diverticulum in a lumbar myelogram does not usually mean complete avulsion of the nerve root, and some recovery may be anticipated. The neurological deficit in two of the four cases did not correspond segmentally to the location of the diverticula.