Magnifying colonoscopy can be used to observe colonic mucosal pits. Using this technique, a pit pattern classification system consisting of seven categories has been established. We evaluated the role of magnifying colonoscopy for the diagnosis of colorectal tumors, particularly for the assessment of the invasion depth of early colorectal carcinoma, which is an important indicator for successful and complete endoscopic resection. Thirty-two of early colorectal cancers in twenty-seven cases were examined by magnifying colonoscopy using 0.05％ crystal violet solution. The main and accessory pit patterns of all of the lesions were classified by magnifying colonoscopy. The depth of vertical invasion of the tumor was also assessed by endoscopic ultrasonography as well as by histological examination following endoscopic mucosal resection or surgical operation. An accurate determination of tumor depth by magnifying colonoscopy was possible in 84.3％ of the cases, compared to 78.1％ that were properly diagnosed by endoscopic ultrasonography.