Staged bilateral hip arthroplasties were carried out in two patients with osteoarthritis of the hip secondary to the development of hip dysplasia in Hereditary Multiple Exostosis (HME).Both patients had near ankylosis of their hips with pain and difficulty in performing activities of daily living. A proximal femur replacing prosthesis was implanted through an extended trochanteric osteotomy, with preservation of as much proximal bone stock as possible. At latest followup (two to five years), there was a sustained improvement in range of motion and symptoms. The Harris Hip Scores improved from 25 and 31 to 83 and 78. The Toronto Extremity Salvage Scores improved from 49% and 55% to 88% and 75%. Radiographs show bony ingrowth and healing of the trochanteric fragments. In severe HME, hip arthroplasty with replacement of the proximal femur provides good symptomatic relief and return of hip joint movement.