Three episodes of sciatic nerve palsy occurred after open reduction and internal fixation of a fracture-dislocation of the left hip and pelvis in a 20-year-old female injured in a motor cycle accident. There were also ipsilateral open fractures of the tibia and fibula and an open knee injury. When the palsy first developed the patient was in a hip spica plaster cast extending from the costal margin to encase the whole left lower limb. At the time of the second and third episodes of palsy she was in a left below-knee cast and it was not possible to fully assess the function of involved muscles clinically or electromyographically. Psychological factors due to prolonged disability and hospitalization were suspected as a possible cause of weakness. Therefore evoked potentials obtained by stimulation of the peroneal nerves were used to aid diagnosis. There was no response from lumbar and cerebral recording sites on stimulation of the peroneal nerve on the affected side. Diagnosis of a conduction block in the sciatic nerve was thus established. The patient recovered clinically and on repeated testing after motor recovery the cortical potential was attenuated and delayed by 15ms. Recurrent sciatic nerve palsy, occurring three times after hip trauma and with heterotopic bone formation and diagnostic application of evoked potential techniques, has not been previously reported.