e14114 Background: Background: Conflicting results have been reported whether pre diagnosis diabetes mellitus (DM) influence survival of colorectal cancer patients or not. Therefore, we determine the influence of DM on long-term outcomes of stage 1-3 patients with resected colon and rectal cancer. Methods: This prospective study include a total of 4,131 participants who were treated for cancer between 1995 and 2005 in South Korea in a single hospital (Non DM: 3,614 patients, DM: 517 patients) with average follow up period of 12 years. We analyzed differences in all cause mortality, disease free survival (DFS), recurrence free survival (RFS) and colorectal cancer-specific mortality between colorectal patients with DM and those without DM. Results: After adjustment for potential confounders, pre-diagnosis DM significantly associated with increased all cause mortality (HR: 1.46, 95% CI: 1.11-1.92), and recurrence free survival reduced DFS (HR: 1.45, 95%CI: 1.15-1.84) and RFS (HR: 1.32, 95% CI: 0.98-1.76) in colon cancer patients but not in rectal cancer patients. In colon cancer patients, DM negatively affects the survival outcome of proximal colon cancer (HR: 2.08, 95%CI: 1.38-3.13), but not of distal cancer (HR:1.34, 95% CI: 0.92-1.96). Conclusions: To our knowledge, the current study first reported the effects of pre-diagnosis DM on survival outcome of colorectal cancer are site specific (proximal colon, distal colon and rectum). The current study was supported by the National Research Foundation of Korea (KRF) (No. 2011-0004892) and the National R&D Program for Cancer Control, Ministry of Health & Welfare, Republic of Korea (1120230). [Table: see text]