Previous cohort studies have demonstrated a positive association between diabetes mellitus (DM) and colorectal cancer (CRC). However, there are few comparisons between groups with controlled DM and uncontrolled DM. This study examined associations between diabetes as defined by fasting serum glucose (FSG) levels and self-reported history of DM and CRC risk among Korean adults. Data from the Korean Multi-center Cancer Cohort between 1993 and 2005 were analyzed. The study population comprised 14,570 participants aged 20 years or older. Participants were followed until December 31, 2012 (median follow-up: 11.9 years). Among participants with high FSG (≥126mg/dL), the risk of developing CRC was significantly higher (HR: 1.51 [1.02-2.25]) than among participants with low FSG (<126mg/dL). Risk was not significantly higher among participants with self-reported history of DM (HR: 1.34 [0.78-2.31]). When both FSG and history of DM were considered together, the risk of CRC was higher among participants with both high FSG and no history of DM (HR: 1.54 [0.97-2.43]), but was not significantly higher among participants with both high FSG and a history of DM (HR: 1.50 [0.73-3.05]). When the first 5 years of follow-up were excluded, among participants with high FSG, the risk of developing CRC was significantly higher (HR: 1.61 [1.02-2.56]) than among participants with low FSG. Risk of CRC was also significantly higher among participants with high FSG and no history of DM (HR: 1.69 [1.01-2.84]). High FSG and self-reported history of DM were associated with increased risk of CRC in this Korean population.