Purpose. To evaluate the clinical and radiologic midterm results of rotational acetabular osteotomy (RAO) in incongruent hip joints. Material and Methods. A consecutive series of 15 hips in 14 patients who underwent RAO in incongruent hip joint were evaluated at an average follow-up of 52.3 months (range from 36 to 101 months). The average age at operation was 27 years (range from 12 to 38 years) old. The preoperative diagnoses were developmental dysplasia in 4 hips, sequelae of Legg-Calvé-Perthes disease in 8 hips, and multiple epiphyseal dysplasia in 3 hips. The RAO procedures were combined with a femoral valgus oseotomy in 10 hips, advance osteotomy of greater trochanter in 4 hips, derotational osteotomy in 2 hips. Clinically, Harris hip score, range of motion, leg length discrepancy(LLD) and hip joint pain were evaluated. Radiological changes of anterior and lateral center-edge(CE) angle, acetabular roof angle, acetabular head index(AHI), ratio of body weight moment arm to abductor moment arm, and a progression of osteoarthritis were analyzed. Results. The Harris hip score ha been improved from average from 67.5 points preoperatively to 97.6 points postoperatively. There have been no significant changes in the range of motion. The anterior CE angle increased from an average of 9.0°(-19.7□18.6°) to 32.5°(22.6□39.1°), the lateral CE angle from 7.6°(-12.1□14.1)° to 31.7°(26.5□37.8°) and the AHI from 61%(33□73%) to 86%(65□100%). The average ratio of body weight moment arm to abductor moment arm was changed 1.88 to 1.49. There was no case showing progression of osteoarthritis. None of the patients experienced revision surgery. Conclusion. The conventional salvage operation, such as Chiari osteotomy, has been recommended in incongruent hip. However, if we can expect to have a congruency after RAO with/without any femoral osteotomies, it would be a hopeful procedure for the incongruent joints by enhancing acetabular coverage, taking joint surface with normal articular cartilage, increasing abductor moment arm with additional improvement in LLD