Post-traumatic and post-operative leg-plexus paresis is often misdiagnosed as sciatic or femoral paresis and thus falsely thought to be rare. In 20 post-traumatic cases the cause was predominantly or exclusively due to sacral plexus damage, with paralysis of the muscles innervated by the sciatic nerve and of the gluteal muscles. The most frequent cause was severe pelvic trauma with ring fracture of the pelvis, separation of the symphysis and iliosacral gap or fracture of the hip joint. Postoperative leg-plexus paresis was noted in eight cases after total hip-joint replacement (predominantly damage to the lumbar plexus) and twice after operatively treated fracture of the acetabulum. Both pressure and tearing lesions can be the basic cause.