The treatment of acetabular dysplasia in adolescents (age> 12) is difþcult and various complex pelvic osteotomies have been described. The aim of surgery being improvement in pain and to delay the onset of secondary osteoarthrosis. Methods: We present our experience of using the Tonnis triple pelvic osteotomy for treatment of acetabular dysplasia in the adolescent and adult age groups (range 13–27 years). This retrospective analysis includes 25 patients operated on over a nine year period (1991–2000) with an average followup of four years (range 2–8 years). More than 50% of the patients had had a previous open reduction or femoral osteotomy for CDH. Results: Radiographic analysis (pre & post op) included CE angle of Wiberg, Sharp-Ullmann index and the acetabular angle of the weight bearing zone. All parameters showed an improvement in the post operative analysis with an improvement in pain and range of movement in all patients. Discussion: The Tonnis triple pelvic osteotomy has the advantage of allowing the operator a direct þeld of view at all times and achieving a great deal of lateral rotation and medial displacement of the acetabulum due to the proximity of the osteotomy to the acetabulum. The ischial ramus and its ligaments to the sacrum are left intact, leading to greater stability of the pelvis and spine. Conclusion: Though technically difþcult and needing a long learning curve, it does improve acetabular alignment and symptoms in the early postoperative years. However long term studies are required to document its effect on the rate of secondary osteoarthrosis.