A new triple osteotomy, polygonal pelvic osteotomy (PPO), is described for use in dysplastic hips. The hip joint must be congruous with a centre-edge (CE) angle between +20 degrees and -10 degrees. Templates are used before and during operation which allow precise correction of the position of the acetabulum. The geometry of the osteotomy and a special compression plate achieve sufficient stability to permit early mobilisation. Surgery is indicated in adolescents and young adults if pain persists for at least two months. The surgical exposure, operative technique and postoperative management are presented, with the two-year results in nine cases.