['Rotational acetabular osteotomy (RAO) is one of the surgical procedures for painful dysplastic hips. Although several risk factors for poor outcome of RAO have been reported, the presence of a curtain osteophyte in the acetabulum has not been evaluated as a possible risk factor. This study aimed to analyze the risk factors affecting the outcome of RAO and to clarify whether curtain osteophytes are one of the risk factors.', 'We retrospectively analyzed 87 hips in 78 patients with a mean age of 36 (range, 13-54) years. The mean follow-up period was 8.3 (range, 2.1-19.5) years. The radiographic severity of osteoarthritis was classified into four stages: pre-arthrosis, initial stage, advanced stage, and terminal stage. The Japanese Orthopaedic Association (JOA) hip score was used for clinical evaluation. Poor outcome was defined as a hip with a JOA score\u2009<\u200980 points or terminal-stage osteoarthritis at final follow-up. Several factors were evaluated by logistic regression analysis.', 'At final follow-up, ten hips had a JOA score\u2009<\u200980 and nine hips had progressed to terminal-stage osteoarthritis. Since five hips had a JOA score\u2009<\u200980 as well as terminal-stage osteoarthritis, a total of 14 hips were determined to have poor outcome. An additional ten\xa0years of age at surgery, pre-operative minimal joint space\u2009<\u20092\xa0mm, presence of a curtain osteophyte, and fair/poor congruency in abduction were identified as significant risk factors for poor outcome of RAO.'] Are curtain osteophytes one of the risk factors for the poor outcome of rotational acetabular osteotomy?