A new periacetabular osteotomy of the pelvis has been used for the treatment of residual hip dysplasias in adolescents and adults. The identification of the joint capsule is performed through a Smith-Petersen approach, which also permits all osteotomies to be performed about the acetabulum. This osteotomy does not change the diameter of the true pelvis, but allows an extensive acetabular reorientation including medial and lateral displacement. Preparations and injections of the vessels of the hip joint on cadavers have shown that the osteotomized fragment perfusion after correction is sufficient. Because the posterior pillar stays mechanically intact the acetabular fragment can be stabilized sufficiently using two screws. This stability allows patients to partially bear weight after osteotomy without immobilization. Since 1984, 75 periacetabular osteotomies of the hip have been performed. The corrections are 31 degrees for the vertical center-edge (VCE) angle of Wiberg and 26 degrees for the corresponding angle of Lequesne and de Seze in the sagittal plane. Complications have included two intraarticular osteotomies, a femoral nerve palsy that resolved, one nonunion, and ectopic bone formation in four patients prior to the prophylactic use of indomethacin. Thirteen patients required screw removal. There was no evidence of vascular impairment of the osteotomized fragment.