Objectives: The objective of this study was to analyse the changes produced in each of the five variables of the Peer Assessment Rating (PAR) index in patients treated with the Invisalign System. Methods: In total, 77 patients (23 males and 54 females) with a mean age of 37.7 years (standard deviation 12.7), attending a private office and treated with the Invisalign System were selected. The same operator treated all patients. Initial and final virtual models obtained by the intraoral scanner iTero were selected. Using the Ortocad programme, the five parameters of the PAR index were measured in the virtual models: maxillary/mandibular anterior segments alignment, posterior occlusion, overjet, overbite, and discrepancy of the centre line. The degree of improvement was calculated from the differences between the initial and final PAR values. Results: Measurement reproducibility results showed an intra- observer coefficient of variation lower than the inter-observer coefficient (1.2% and 2.1%, respectively). The intra-class coefficient was 0.98 for intra-observer measurements and 0.91 for inter-observer measurements. 44.2% of the sample varied their PAR index in less than 10 points, 36.4% between 11 and 20 points, 14.3% between 21 and 30 points, and 5.2% decreased by almost 40 points in the PAR index. The total mean variation of the initial and final PAR index in patients treated with the Invisalign System was 13 points, an improvement of 57%. Conclusion: The variables of the PAR index with the greatest improvement after Invisalign System treatment were maxillary/ mandibular anterior segments alignment, overjet, overbite, and discrepancy in the centre line. Keywords: Invisalign, PAR, Peer Assessment Rating index