This paper describes the rationale and technique for a combined procedure of transtrochanteric rotational osteotomy and vascularized iliac bone grafting in cases of osteonecrosis of the femoral head with an extensive and widely collapsed necrotic lesion in young patients. The authors performed this combined operation for 12 joints in 12 patients over 14 years from 1984 until 1997. At a mean of 81 months after the operation, in eight patients who had no pain, the average Harris hip score was 90.0 points. Postoperative radiographic evaluation revealed that collapse (more than 2 mm) of the femoral head was prevented in ten patients. Conversion to an endoprosthesis was avoided in all patients except one in this series. The authors recommend this procedure for advanced and extensive osteonecrosis of the femoral head, especially in young patients, to preserve the joint, even though it is a relatively complex procedure.