Abstract:[Objective] To introduce the surgical technique of modified Stoppa approach combined with iliac spine approach for periac- etabular osteotomy. [Methods] Periacetabular osteotomy through modified Stoppa approach combined with iliac spine approach was per- formed in 3 patients for adult developmental hip dysplasia, including 1 case with unilateral involved and 2 cases with bilateral affected, in our department from 2018 to 2019. Before operation a 3D printed pelvic model was made to measure the lateral center edge angle (LCE) , anterior center edge angle (ACE) and Tonnis angle, additionally, mimic the osteotomies preoperatively. In the real operation, a Stoppa inci- sion on the middle of the abdomen was made to expose the rectus abdominis sheath, separate the rectus abdominis along the white line, ex- pose the suprapubic branch and the quadrilateral along the extraperitoneal space. Locating the acetabulum with guide pins, the pubis and quadrilateral osteotomies were conducted. After that, an iliac spine approach was made to expose the anterior superior iliac spine and the ili- ac plate, iliac osteotomy in the direction of the ischial notch was done, and then rotate the osteotomy block, fix it with 4 cortical screws. [Results] All the 3 patients had osteotomies performed successfully without complications, such as vascular and nerve injuries. The LCE and ACE increased significantly, whereas the Tonnis angle decreased significantly postoperatively compared with those preoperatively (P＜ 0.05) . At 6 weeks after the operation, all the 3 patients resumed walking with a single crutch. By the time 12 weeks after surgery, the Xrays showed the osteotomy completely healed, and all the patients returned to walking with full weight bearing without crutches. [Conclusion] This surgical technique can perform osteotomy of the pubic ramus, posterior acetabular column and quadrilateral under direct vision, avoiding the risk of intraoperative osteotomy penetrating the joint.