We reviewed the results of 3126 consecutive total hip replacements and identified postoperative neuropathy in the ipsilateral lower extremity after fifty-three (1.7 per cent) over-all and after 1.3 per cent of the primary arthroplasties. The prevalence was 5.2 per cent after the primary arthroplasties that had been done for congenital dislocation or dysplasia of the hip and 3.2 per cent after the revisions (all diagnoses). Thus, these two types of operations were risk factors (p less than 0.01). Limb-lengthening only partially accounted for the increased prevalence of neuropathy after these procedures. The sciatic nerve was involved in all but five extremities. The cause of the palsy was unclear or unknown in thirty (57 per cent) of the extremities. When the patients were last seen, at a minimum of one year and a maximum of sixteen and one-half years after the operation, seven extremities were normal neurologically, thirty-three had a mild neurological deficit, and thirteen had a major deficit. All patients who had complete recovery of neurological function had it by twenty-one months. Of thirty-six extremities that were evaluated at a minimum of twenty-four months after the operation, seven were neurologically normal, twenty-three had a mild persistent deficit, and six had a major persistent deficit. The ability to walk decreased for all patients who had a nerve palsy. The greatest disability was in the patients who had been forty-eight years old or less and had had a primary total hip replacement (p = 0.037). The prognosis for neurological recovery was related to the degree to which the nerve was damaged.(ABSTRACT TRUNCATED AT 250 WORDS)