Background: Many successful osteotomies have been reported for the treatment of acetabular dysplasia. However, triple pelvic osteotomy remains a technically challenging procedure with potential for significant complications. This study examined a series of Tönnis periacetabular osteotomy (TPAO) procedures performed using the modified Stoppa approach to treat acetabular dysplasia in adolescents. Objective: To describe the radiographic outcomes, complications, and early functional results of TPAO using the modified Stoppa approach for acetabular dysplasia in adolescents. Methods: This study included 16 patients (20 hips) who underwent TPAO using the modified Stoppa approach for symptomatic acetabular dysplasia. The characteristics of the patients and the surgical procedure were discussed. The radiologic outcome was evaluated using the lateral center-edge (CE) and Tönnis roof angles. Perioperative data including surgery duration, blood loss, and complications were recorded. Complications were also discussed. Results: The mean age of the patients was 11.5±1.1 (10 to 13) years. The mean preoperative anteroposterior CE angle was 14.7±3 degrees (7 to 19 degrees), and the mean postoperative angle was 35.7±3.1 degrees (30 to 42 degrees; P<0.001). The mean preoperative Sharp’s angle was 55.9±5.4 degrees (48 to 65 degrees), and the postoperative mean was 33±5 degrees (24 to 40 degrees; P<0.001). The mean Tönnis angle before and after osteotomy was 23.3±7.1 degrees (17 to 36 degrees) and 7.1±2 degrees (4 to 10 degrees), respectively (P<0.001). The mean operative time was 42.2±10.3 minutes with a mean blood loss of 167.7±50.3 mL. One patient sustained a bladder injury as a major complication. Conclusions: The use of TPAO with the intrapelvic modified Stoppa approach in the treatment of hip dysplasia provides the benefits of a single incision, access to 2 hips in the same session, positional advantage, and abductor function preservation. Early results are satisfactory and safe. Level of Evidence: Level IV.