Background/Aims: Although the diagnostic value of fluorine-18 2-fluoro-2-deoxy-D-glucose (F-18-FDG) positron emission tomography/computed tomography (F-18-FDG-PET/CT) in patients with colorectal cancer (CRC) has been reported, the association between the F-18-FDG uptake in metastatic lymph nodes (FDGLN) and clinicopathological variables has not been fully investigated. We evaluated the diagnostic value of F-18-FDG-PET/CT in detecting LN metastasis from CRC, and the relationship between F-18-FDG-PET/CT-detecting LN metastasis and prognosis. Methods: We retrospectively analyzed the medical records of 370 patients who underwent preoperative F-18-FDG-PET/CT, followed by surgical resection for CRC between January 2007 and December 2010. We analyzed the sensitivity, specificity, and accuracy of F-18-FDG-PET/CT and CT in diagnosing metastatic LNs. Survival was analyzed in 115 patients with stage III CRC. Results: The sensitivity, specificity, and accuracy for detecting metastatic LNs using F-18-FDG-PET/CT were 56.8, 90.3, and 74.2%, and those for contrast-enhanced CT were 38.4, 95.5, and 65.0%, respectively. The accuracy of F-18-FDG-PET/CT was significantly associated with tumor depth and lymphatic involvement. In the survival analysis, cancer-specific survival and the disease-free survival were significantly shorter in patients with stage III CRC with FDGLN than in those without FDGLN. Conclusion: F-18-FDG-PET/CT had low sensitivity and high specificity for detecting metastatic LNs from CRC. FDGLN independently predicted poor prognosis in patients with stage III CRC.