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The role of hip arthroscopic surgery in dysplasia is controversial.To determine the 7-year joint preservation rate after hip arthroscopic surgery in hip dysplasia and identify anatomic and intraoperative features that predict the success of hip preservation with arthroscopic surgery, allowing the formulation of an evidence-based classification system.Case-control study; Level of evidence, 3.Between 2008 and 2013, 111 hips with dysplastic features (acetabular index [AI] >10° and/or lateral center-edge angle [LCEA] <25°) that underwent arthroscopic surgery were identified. Clinical, radiological, and operative findings and the type of procedure performed were reviewed. Radiographic evaluations of the operated hip (AI, LCEA, extrusion index) were performed. Outcome measures included whether the hip was preserved (ie, did not require arthroplasty) at follow-up and the preoperative and postoperative Non-Arthritic Hip Score (NAHS) and Hip disability and Osteoarthritis Outcome Score (HOOS). The AI and LCEA were calculated, factored by a measure of articular wear (AIf and LCEAf, respectively), according to the University College Hospital, London (UCL) grading system as follows:AIf = AI × (number of UCL wear zones + 1), and LCEAf = LCEA / (number of UCL wear zones + 1).A contour plot of the resulting probability value of failure for every combination of AIf and LCEAf allowed for the determination of the zones with the lowest and highest incidences of failure to preserve the hip.The mean AI and LCEA were 9.8° and 18.0°, respectively. At a mean follow-up of 4.5 years (range, 0.4-8.3 years), 33 hips had failed, requiring hip arthroplasty. The 7-year joint survival rate was 68%. The mean improvements in the NAHS and HOOS were 11 (P = .001) and 22.8 (P < .001) points, respectively. The zone with the greatest chance of joint preservation (odds ratio, 10; P < .001) was the green zone, with an AIf of 0° to 15° and an LCEAf of 15° to 25°; in contrast, the zone with the greatest chance of failure (odds ratio, 10; P < .001) was the red zone, with an AIf of 20° to 100° and an LCEAf of 0° to 10°.Overall, the 7-year hip survival rate in hip dysplasia appears inferior compared with that reported in femoroacetabular impingement (78%). Hip arthroscopic surgery is associated with an excellent chance of hip preservation in mild dysplasia (green zone: AI = 0°-15°, LCEA = 15°-25°) and no articular wear. The authors advise that the greatest caution should be used when considering arthroscopic options in cases of severe dysplasia (red zone: AI >20° and/or LCEA <10°).