Thirty-seven consecutive patients who were more than seventy-five years old and had an unstable intertrochanteric or subtrochanteric fracture were treated by primary bipolar arthroplasty from 1983 through 1986. The functional results, according to the rating scale of Merle d'Aubigné, were rated as good or excellent in 75 per cent of the patients and remained almost unchanged with time. Roentgenographic follow-up showed early bone formation around the extramedullary part of the femoral component. The results in this prospective group of patients were compared with those in a similar but retrospective control group of forty-two patients who were treated by internal fixation from 1979 through 1982 and in whom early full weight-bearing was not possible. In the bipolar arthroplasty group, rehabilitation was easier and faster, and the incidences of pressure sores, pulmonary infection, and atelectasis were significantly lower (p less than 0.05). The early walking with full weight-bearing that the bipolar arthroplasty made possible is considered to be a major contributing factor to these results.