PURPOSE: Since 2004, the National Cancer Screening Program of Korea has included colorectal cancer screening based on primary screening with the fecal occult blood test (FOBT). We report on the clinical features of colorectal cancer detected by the National Cancer Screening Program. METHODS: We retrospectively analyzed 577 patients who underwent elective surgery for colorectal cancer at the Seoul National University Hospital between January 2008 and December 2009. We compared the clinical features of colorectal cancers detected by the National Cancer Screening Program (NCSP group) with those of the control group in terms of age, gender, preoperative symptom, location of the tumor, surgical technique and tumor-node-metastasis (TNM) stage. RESULTS: Age, gender, location of the tumor and operation types were not different between the two groups. The proportion of asymptomatic patients was significantly higher in the NCSP group than it was in the control group (86.5% vs. 20.0%; P < 0.001). The proportion of less invasive lesions (T1 or T2) was significantly higher in the NCSP group (46.3% vs. 27.7%; P = 0.002). The pathologic stages of the colorectal cancers in the NCSP group were I, 40.3%; II, 17.9%; III, 40.3% and IV, 1.5% whereas in the control group, they were I, 20.8%; II, 32.9%; III, 34.9% and IV, 11.4%. The proportion of stage I cancer was significantly higher in the NCSP group than in the control group (40.3% vs. 20.8%; P = 0.006). CONCLUSION: Our study demonstrates the FOBT in the NCSP is effective in early detection of colorectal cancer.