Since 1969 the authors have been developing a technique of posterior rotation osteotomy based on the concept of L. Molé as a conservative treatment for avascular necrosis of the femoral head in the adult. The technique consists of rotating the head round the axis of the neck so as to displace the necrotic bone from the weight bearing area to the posterior part of the joint. It is a safe procedure which leaves the joint undisturbed, the muscles intact and the vessels of the femoral head undamaged. It must be done very precisely to avoid undesirable displacement of the head. Since 1979 the technique has been modified in the light of Sugioka's concepts. It is indicated for grades II and III necroses. Twenty-six cases have been operated on and followed up for a maximum of 15 years. Seventy-five percent of the results were satisfactory as far as pain and function were concerned. The radiographic evaluation has shown no progress of the necrotic zones, but arthrosis, often severe, almost always appeared even though it was clinically silent. Although the procedure does not allow healing of the lesion, it permits conservation of the femoral head for some years and thus delays the need for arthroplasty.