A 60-year-old man presented with diarrhea and weight loss. Colonoscopy revealed multiple reddish polypoid lesions throughout the gastrointestinal tract and was diagnosed as Cronkhite-Canada syndrome (CCS). Prednisolone therapy caused regression of polyps. Some of them were suspected to be early colon cancers and adenomas. We endoscopically performed mucosal resection for 15 polyps after prednisolone therapy. Histological examination of one of polyps showed invasion of the submucosal layer and colon resection was performed. This case suggests that diagnosis and treatment are important in polyps of CCS.