PURPOSE: The aim of this study was to investigate detection of dysplasia or colitic cancer with ulcerative colitis by use of magnifying endoscopic observation. METHODS: From 1986 through 2000, ulcerative colitis was diagnosed and treated in 886 patients at Kitasato University East Hospital. Of the total, we studied 25 patients in depth: 14 who had dysplasia alone, 5 in whom cancer was diagnosed during follow-up after the detection of dysplasia, and 6 who had colitic cancer. RESULTS: Dysplasia was detected in 11 (3.2 percent) of 345 patients with extensive colitis and in 8 (3.7 percent) of 217 with left-sided colitis. Colorectal cancer was diagnosed in nine patients (2.6 percent) with extensive colitis and in two (0.9 percent) with leftsided colitis. Neither dysplasia nor colitic cancer was found in patients with proctitis-type colitis. Endoscopically, dysplasia and early cancer were characterized by granular or nodular protruding mucosa or by lowly protruding or flat mucosa, often associated with redness. Dye-spraying endoscopy was useful for detection. Magnifying endoscopy of ten regions of dysplasia (7 patients) and five early cancers (4 patients) showed IIIS to IIIL type pits or IV type pits. Biopsy of sites showing tumorous pits on magnifying endoscopy revealed dysplasia and early cancer. Observation of the pit pattern was found to be diagnostically useful. CONCLUSIONS: Dye spraying and magnifying endoscopy are useful for the detection, targeted biopsy, and diagnosis of dysplasia and colitic cancer in patients with ulcerative colitis. METHODS: From 1986 through 2000, ulcerative colitis was diagnosed and treated in 886 patients at Kitasato University East Hospital. Of the total, we studied 25 patients in depth: 14 who had dysplasia alone, 5 in whom cancer was diagnosed during follow-up after the detection of dysplasia, and 6 who had colitic cancer. RESULTS: Dysplasia was detected in 11 (3.2 percent) of 345 patients with extensive colitis and in 8 (3.7 percent) of 217 with left-sided colitis. Colorectal cancer was diagnosed in nine patients (2.6 percent) with extensive colitis and in two (0.9 percent) with left  sided colitis. Neither dysplasia nor colitic cancer was found in patients with proctitis-type colitis. Endoscopically, dysplasia and early cancer were or by granular or nodular protruding mucosa or by lowly protruding or flat mucosa, often a Dye-spraying endoscopy was useful for detection. Magnifying endoscopy of ten regions of dysplasia (7 patients) and five early cancers (4 patients) showed IIIS to IIIL type pits or IV type pits. Biopsy of sites showing tumorous pits on magnifying endoscopy revealed dysplasia and early cancer. CONCLUSIONS: Dye spraying and magnifying endoscopy are useful for the detection, targeted biopsy, and diagnosis of dysplasia and colitic cancer in patients with ulcerative colitis.