Patients having long-standing ulcerative colitis (UC) and Crohn's colitis are exposed to the increased risk of colorectal cancer (CRC) [1-3]. Dysplasia, a precancerous lesion of CRC in the patients having long-standing inflammatory bowel disease (IBD), can be categorized into indefinite for dysplasia (IND), low-grade dysplasia (LGD), and high-grade dysplasia (HGD) [4]. Traditionally, total proctocolectomy had been regarded as a standard treatment not only for CRC but also for dysplasia in UC patients [4]. However, since early studies about the feasibility of polypectomy for dysplasia [5,6], subsequent studies have supported endoscopic resection of polypoid dysplasia could be the first choice for the prevention of CRC in IBD, mostly UC patients. The pooled incidence of CRC after endoscopic resection of polypoid dysplasia is 5.3 cases per 1,000 patient-years in the colitic patients [7], and the incidence of post-colonoscopy CRC was 2 cases per 1,000 patient-years according to a recent metaanalysis regarding outcomes after endoscopic resection of dysplasia in colitic patients [8]. Therefore, recent guidelines suggest that endoscopic resection as a key modality for the treatment of visible and endoscopically resectable dysplasia in the colitic patients [9-11]. HISTOLOGIC FEATURES OF DYSPLASIA IN UC By definition, dysplasia is histologically unequivocal neoplastic epithelium without evidence of tissue invasion and can be categorized as followings: negative for dysplasia, indefinite for dysplasia, and positive for dysplasia [12]. IND is applied to epithelial changes showing extraordinary regeneration but not sufficient for an unequivocal diagnosis of dysplasia. Positive for dysplasia can be subdivided into LGD and HGD. Colitis-associated dysplasia frequently shows his-JDCR