Pelvic osteotomies were proposed in order to preserve as much as possible of the acetabular cartilage. The aims were twofold: centering of the head of the femur in the acetabulum, to improve its stability; correction of the delay in growth of the acetabulum: there is a potential correction, allowing for the femoral growth, or a passive correction by widening a deep acetabulum. Two types of osteotomy are proposed: reorientation osteotomies (Salter, triple osteotomy) which have both a mechanical and biological effect and widening osteotomies (Chiari), which are in fact extracapsular arthroplasties. All the techniques of reorientation osteotomy are very similar and achieve a reorientation of the acetabulum on the femoral head by varization, retroversion and, when possible, medialization. The Chiari osteotomy, which is technically difficult, should be performed according to the very precise rules described by Chiari.