AIM: To clarify whether mucosal crypt patterns observed with magnifying colonoscopy are feasible to distinguish non-neoplastic polyps from neoplastic polyps.METHODS: From June 1999 through March 2000, 180consecutive patients with 210 lesions diagnosed with a magnifying colonoscope (CF-200Z, Olympus Optical Co., Ltd., Tokyo, Japan) were enrolled. Magnification and chromoendoscopy with 0.2% indigo-carmine dye was applied to each lesion for mucosal crypt observation.Lesions showing types Ⅰ and Ⅱ crypt patterns were considered non-neoplastic and examined histologically by biopsy, whereas lesions showing types Ⅲ to Ⅴ crypt patterns were removed endoscopically or surgically.The correlation of endoscopic diagnosis and histologic diagnosis was then investigated.RESULTS: At endoscopy, 24 lesions showed a type Ⅰ or Ⅱ pit pattern, and 186 lesions showed type Ⅲ to Ⅴ pit patterns. With histologic examination, 26 lesions were diagnosed as non-neoplastic polyps, and 184lesions were diagnosed as neoplastic polyps. The overall diagnostic accuracy was 99.1% (208/210). The sensitivity and specificity were 92.3% (24/26) and 99.8%(184/186), respectively.CONCLUSION: Magnifying colonoscopy could be used as a non-biopsy technique for differentiating neoplastic and non-neoplastic polyps.