Twenty consecutive rotation osteotomies for idiopathic necrosis of the femoral head with an average followup of 6.5 years were reviewed. The original technique used a nail plate for rotation and fixation of the fragments and proved to be reliable for precision of rotation, osteotomy fusion, and absence of mechanical or vascular complications. There were 16 anterior extension Sugioka osteotomies with 52 degrees average rotation, and four posterior flexion Kempf osteotomies with 77 degrees average rotation. The status of 18 surgically treated hips after 5 years was seven failures, two fair results, and nine satisfactory results. Rotation osteotomies are recommended only when the necrotic zone of the femoral head can be removed from the major weightbearing zone of the acetabulum, when the hip is in extension. In Sugioka's anterior rotation, the necrotic zone, although unloaded in extension, usually remains in contact with the acetabular major bearing zone (40 degrees around apex) in hip flexion. Thus, it is recommended only for Ficat Stage 2 nonflattened heads. In Kempf's posterior rotation, the necrotic zone is unloaded in hip extension and flexion, so Stage 3 is not a contraindication for this osteotomy. In addition, osteotomies are not recommended when the necrosis extends deeper than the proximal third of the femoral head. In these large necroses, there may be an overloading of the healthy part of the rotated head, resulting in its secondary mechanical deterioration. If these conditions are fulfilled, rotation osteotomy of the proximal femur may, in patients younger than 45 years of age, delay for a decade the degradation of hips with idiopathic osteonecrosis.