PURPOSE: As the number of patients with inflammatory bowel disease (IBD) has steadily increased in Korea, IBD-associated cancers are expected to increase in number. This study investigated the clinical features of intestinal cancer in patients with IBD. METHODS: One hundred five patients with ulcerative colitis (UC) and 270 patients with Crohn's disease (CD) under the care of the Department of Colon and Rectal Surgery, Asan Medical Center, between December 1989 and January 2009 were reviewed retrospectively. RESULTS: Ten patients of the 105 with UC and 5 patients of the 270 with CD were found to have intestinal cancer. The mean age was 45 yr (+/-8.8), and the mean duration of IBD at the time of diagnosis of the cancer was 12.6 yr (+/-6.0). Six of the 15 cancer patients had no history of treatment for IBD of more than 3 mo before diagnosis of the cancer. Eleven cancers were located in the rectum (7 in UC, 4 in CD), including 1 case of synchronous cancer. One case of small bowel cancer was found in a patient with small bowel CD. Four cases involved a mucinous adenocarcinoma. Eight of the 12 cases of an adenocarcinoma of the colon and rectum were advanced stage. CONCLUSION: IBD-associated intestinal cancers were found at a relatively young age, were diagnosed at an advanced stage, and had a higher proportion of mucinous adenocarcinomas than in sporadic cancer. Considering the increasing incidence of IBD and the expected increase in the number of IBD-associated cancer in Korea, every effort should be made to prevent intestinal cancer in patients with IBD and to detect it early.