Imaging Diagnosis of Colorectal Cancer Ah Young Kim Department of Radiology, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea. aykim@amc.seoul.kr Abstract Recently, treatment strategy of rectal cancer has undergone a dramatic change. Application of total mesorectal excision and preoperative chemoradiation therapy (PCRT) has become standard procedure for locoregional and locally advanced rectal cancer, respectively. Functional and morphological radiologic evaluation as well as multidisciplinary approach is both essential for planning patient-specific therapy. In other words, the needs for more accurate T-and N-staging and assessment of circumferential resection margin, both before and after PCRT, are increasing rapidly. Although there is no consensus on the role of diagnostic imaging such as endorectal ultrasonography, computed tomography and magnetic resonance imaging (MRI), in evaluation of rectal cancer patient so far, MRI is emerging as an essential imaging modality with superior trssue contrast and multiplanar approach. Key Words: Rectal cancer, Magnetic resonance imaging, CT, Endorectal US