Objective The gross extent of ulcerative colitis (UC) is a recognized risk factor for the development of colitis-related dysplasia and colorectal cancer (CRC). The risk of neoplasia associated with the microscopic extent of colitis is unknown. The aim of this study was to describe the gross and microscopic extent of colitis in patients with UC–related dysplasia/CRC. Methods All patients who underwent colectomy at our institution between 1992–2001 with colitis-related dysplasia/CRC were identified. Histological sections from each colectomy specimen were reviewed for the microscopic extent of colitis and the location of all lesions with dysplasia/CRC. Results Thirty-six patients with colitis-related dysplasia/CRC were identified of whom 30 had slides available for review. Gross pancolitis was identified in 19 patients, though microscopic pancolitis was evident in all 30 patients. Among the 11 patients with only distal gross colitis, 4/15 neoplastic lesions were proximal to the area of gross involvement. Conclusions UC-related neoplasia can occur in areas of the colon not grossly involved with colitis, though it did not occur in any patients without microscopic pancolitis. To devise rational cancer surveillance guidelines, further studies are needed to determine the risk of colitis-related neoplasia in patients with microscopic pancolitis but limited gross disease.