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Objectives Cancer Risk and SurveillancePatients with longstanding extensive ulcerative colitis are at increased risk of developing colorectal cancer. Colonoscopic surveillance is recommended by most authorities in an attempt to reduce the associated mortality. Surveillance relies on the detection of premalignant dysplastic tissue, and where dysplasia is detected, proctocolectomy has historically been and currently remains the management of choice, although there is increasing evidence that adenoma-like dysplastic lesions may safely be resected endoscopically. Detection of Dysplasia in Ulcerative ColitisIn patients without ulcerative colitis, the premalignant dysplastic lesion, the adenoma, usually occurs as a clearly delineated macroscopically visible abnormality. However, in ulcerative colitis there is no clear-cut adenoma±carcinoma sequence. Dysplasia can occur in polypoid lesions, but often appears as a more subtle mucosal irregularity, or may be macroscopically invisible. Because of this, most endoscopists worldwide take multiple random biopsies of flat mucosa. It has been estimated that 33 biopsies are required to provide a 90 % chance of finding the highest degree of dysplasia present [1]. It has been recommended that four random biopsies per site over nine sites throughout the colon be undertaken, with increased sampling from the rectosigmoid and with additional biopsies from raised or suspicious lesions [2]. However, it is time-consuming to take 30 ± 50 nontargeted random biopsies throughout the colon, and dysplastic lesions might still be overlooked.Recent improvements in endoscopic equipment and technique, particularly the use of dyesprays (chromoendoscopy), have improved dysplasia detection in ulcerative colitis [3 ± 5],

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