Objective This retrospective study was designed to evaluate the clinical treatment outcomes of borderline cases with Angle class Ⅱ division 1 malocclusion by using peer assessment rating（PAR） index to assess the occlusal traits of pre- and post-treatment models. Methods The subject of this study consisted of borderline patients with Angle class Ⅱ division 1 malocclusion, including 83 children（26 patients with extraction and 57 patients without extraction）. PAR index was used to assess the occlusal traits of dental models before and after orthodontic treatment to evaluate the clinical treatment outcomes of these two groups. Results In borderline cases with Angle class Ⅱ division 1 malocclusion, regardless of extraction or not, the weighted PAR index was decreased after treatment, the percentage reduction in weighted PAR index was more than 70%, and no significant difference exists between extraction and non-extraction group. In the evaluation of orthodontic treatment outcome, 96.39%（80/ 83） of cases improved. Conclusion Borderline cases with Angle class Ⅱ division 1 malocclusion in children no matter extraction or non-extraction, both can achieve good outcomes in occlusion after treatment.
