This study describes the feasibility of magnifying colonoscopy with indigo carmine dye contrast to distinguish neoplastic and nonneoplastic colonic polyps. This study sampled consecutive patients undergoing colonoscopy using an Olympus CF240ZI from January to October 2000 at Chang-Gung Memorial Hospital, Lin-Kou Medical Center. This study analyzed a total of 270 polyps. Indigo carmine (0.2%) was sprayed directly on the mucosa surface before observing the crypts using a magnifying colonoscope (1.5x-100x). The pit patterns were described using the classification proposed by Kudo. Finally, polypectomy or biopsy was performed for histological diagnosis. The study identified 155 adenomas, 99 hyperplastic polyps, 9 adenocarcinomas, and 7 other nonneoplastic lesions (harmatoma, inflammatory polyps, and mucosal tag). The pit pattern was analyzed for all lesions. Further classification into neoplastic (adenoma and adenocarcinoma) and nonneoplastic (hyperplastic and others) polyps revealed 156 neoplastic and 14 nonneoplastic polyps among the type III to type V pits and 92 nonneoplastic and 8 neoplastic polyps among the type I and II pits. The sensitivity of type III to type V pits in detecting neoplastic polyps was 95.1%, with a specificity of 86.8% and diagnostic accuracy of 91.9%. The positive likelihood ratio was 7.3, and the negative likelihood ratio was 0.06. Magnifying colonoscopy with indigo carmine dye contrast provides morphological detail that correlates well with polyp histology. Small flat lesions with typical type II pit pattern should have minimal neoplastic risk, thus endoscopic resection is not necessary.