Abstract Background: Facial and smile attractiveness are significant motivating factor for patients to seek orthodontic treatment. Although there is a general belief that orthodontic treatment improves facial appearance, this has yet not been systematically evaluated. Objectives: To assess the current evidence on the effect of orthodontic treatment on facial attractiveness. Search Methods: Systematic and unrestricted search of nine databases were performed up to January 2022. Selection Criteria: Studies evaluating facial attractiveness before and after orthodontic treatment. Data Collection and Analysis: Extracted data included study design and setting, sample size and demographics, malocclusion type, treatment modality and method for outcome assessment. Risk of bias was assessed with the ROBINS-I tool for non-randomised studies and with RoB-2 for randomized controlled trials. Random-effects meta-analyses of mean differences and their 95% confidence intervals (CIs) were performed. Results: Twenty studies were included in data synthesis; three randomized controlled clinical trials and 17 non-randomized clinical studies of retrospective or prospective design. One of the randomized controlled trials was found to have low risk of bias, one presented some concerns and the third showed a high risk of bias. All non-randomized studies showed either unclear or high risk of bias. Data syntheses showed that orthodontic treatment improved facial attractiveness ratings by 9% when compared to untreated controls (MD: 9.05 / 95% CI: 4.71; 13.39). A combination of orthodontics and orthognathic surgery also showed a positive effect of 5.5% (MD: 5.51 / 95% CI: 1.55; 9.47) when compared to orthodontic treatment alone. There was no difference in effect between extraction and non-extraction treatments (MD: -0.89 / 95% CI: -8.72; 6.94) or between different types of Class II correctors (MD:2.21 / 95% CI: -16.51; 20.93). Limitations: With the exception of 2 RCTs, included studies were of unclear or low quality. Conclusions: Orthodontic treatment has a clinically weak effect on facial attractiveness when compared to no treatment. The same is true when a combined orthodontic/surgical treatment is compared to orthodontics alone. Registration: PROSPERO #: CRD42020169904 Conflict of Interest: None Funding: None