Recent development of dignostic tools such as video-endoscopy, chromoscopy, magnifying endoscopy, and endoscopic ultrasonography has made it possible to do the accurate staging of colorectal cancer. Dysplasia confined to mucosa or upper one-third of submucosa of rectal wall can be treated with mucosal resection or local resection for cure. The involvement of perirectal lymph node by cancers can be confirmed by endoscopic ultrasonography-guided fine needle aspiration cytology (EUS-FNA). Positron emission tomography is useful for the detection of recurrent and metastatic tumor after surgical resection. Colonoscopy is cost-effective for the screening of cancer, however, But the virtual colonoscopy with MR or CT can play the role of colonoscopy without risk. Stool DNA test is a promising tool. In addition to traditional diagnostic tools such as colonoscopy, CT and pathology, emerging knowledge from molecular biology of cancer gives information on predicts the prognosis of colorectal cancer patients.