PURPOSE: To analyse unusual radiologic manifestations of colonic adenocarcinoma, and to correlate these with pathologic findings. MATERIALS AND METHODS: Radiologic findings of ten patients with atypical adenocarcinoma ofthe colon were retrospectively evaluated. The unusual radiologic findings were difined as terminal ileal involvement of the cecal mass, long segmental involvement of over 9cm, and exophytic tumor growth. radiologic and sonographic findings were compared with pathologic specimens obtained from surgical resection. RESULTS: Involvement of the terminal ileum was noted in three cases, long segmental involvement of over 11cm in five cases, and exophytic mass in two. Of three cases with thickening of the terminal ileum, two revealed the infiltration of cancer into the terminal ileum through the ileocecal valve, and the other revealed vascular congestion and edemaon microscopic examination. Five cases with long segmental involvement of over 11cm comprised one of cancer totally infiltrated through the submucosal and proper muscle layer, one of inflammatory thickening distal to thecancer, two of inflammatory change of pericolic fat and serosal adhesion and one of a large intraluminal fungatingmass. In the cases of exophytic mass, one with a larger extraluminal and a smaller intraluminal component revealed necrosis and abscess on pathologic examination, accounting for low attenuation on CT, whereas the other, with exophytic growth, disclosed abundant pools of mucin, resulting in low attenuation on CT. These two cases could notbe differentiated from submucosal tumors. CONCLUSION: Atypical colon cancer may have various manifestations, suchas thickening of the terminal ileum, involvement of a long segment, and an exophytically growing mass. An appreciation of the radiologic findings of this cancer may therefore help in differential diagnosis in cases simulating colitis or submucosal tumors of the colon, such as lymphoma or leiomyoma.