Five colitic cancers were detected among 40 patients with longstanding total colitis. The colitic cancers did not show the common polypoid or ulcerated appearance in the early stage, often being flat or plaque-like. It was not easy to detect these lesions endoscopically, and it was often impossible to do so radiologically. The flat or plaque-like early cancers were often surrounded by granular and/or red mucosa. We believed that the colonoscopic detection of this colitic cancer and dysplasia was difficult because: (1) the morphology of the lesions was difficult to determine, (2) the background mucosa was not normal. When the lesions were small, it was more difficult to detect them on the colitic mucosa than on the normal mucosa. The contrast between the lesion and the background mucosa was not clear in the latter condition. In surveillance colonoscopy (using a TV colonoscope) for longstanding ulcerative colitis, careful scrutiny throughout the large intestine is required to detect colitic cancers and dysplasia at an early state.