Surveillance postendoscopic resection (post-ER) currently warrants biopsies from the resection site scar in most cases, although clinical practice is variable. A classification with standard criteria for scars has not yet been established. We aimed to create and validate a novel classification for post-ER scars by using specific criteria based on advanced imaging.Key endoscopic features for scars with and without recurrence were color respectively as (1) dark brown color, (2) elongated/branched pit pattern and (3) dense capillary pattern; and (1) whitish, pale appearance, (2) round/slightly large pits and (3) irregular sparse vessels. Scars were first assessed with high-definition white light endoscopy (HDWLE) followed by interrogation with NBI. Scars with at least 2 concordant characteristics were diagnosed with "high confidence" for NBI-SCAR. The final endoscopic predictions were correlated with histopathology. Primary outcome was the difference in sensitivity between NBI-SCAR and HDWLE predictions. Secondary outcomes included the validation of our findings in 6 different endoscopy settings (Australia, United States, Japan, Brazil, Singapore, and Malaysia). The validation took place in 2 sessions separated by 2 to 3 weeks, each with 10 one-minute videos of post-ER scars on uNBI-DF. Inter- and intra-rater reliability were calculated with Fleiss' Free-Marginal Kappa and Bennet's S score, respectively.One hundred scars from 82 patients were included. Ninety-five scars were accurately predicted with high-confidence by NBI-SCAR in the exploratory phase. NBI-SCAR sensitivity was significantly higher compared to HDWLE (100% versus 73.7%, p<0.05). In the validation phase, similar results were found for endoscopists who routinely perform colonoscopies and use NBI (sensitivity of 96.4%). The inter- and intra-rater reliability throughout all centers were respectively substantial (k=0.61) and moderate (average S=0.52), for routine colonoscopists who use NBI.NBI-SCAR classification has a high sensitivity and NPV for excluding recurrence for endoscopists experienced in colonoscopy and NBI. In this setting, this approach may help accurate evaluation or resection scars and potentially mitigate the burden of unnecessary biopsies.