BACKGROUND/AIMS: Recent guidelines strongly recommend that the interval of surveillance colonoscopy be determined according to the risk stratification obtained at index colonoscopy. However, because of the differences in perception of the classification of colorectal intraepithelial neoplasia between Asian and Western countries, there is some confusion about surveillance colonoscopy. The aim of the present study was to evaluate the clinicopathological characteristics and the interval of surveillance colonoscopy between patients with high-grade dysplasia/carcinoma in situ and those with intramucosal carcinoma. METHODS: From January 2003 to June 2010, 727 patients were included from 8 tertiary centers. Four hundred fifteen patients (57.1%) had high-grade dysplasia/carcinoma in situ (group A), and 312 (43.9%) had intramucosal carcinoma (group B). Clinicopathological data were reviewed retrospectively. RESULTS: Group A had a significantly more frequent family history of colorectal cancer (3.1% vs. 0.6%, P<0.001), smaller polyp size (12 mm vs. 15 mm, P=0.001), and more proximal location (31.1% vs. 21.8%, P=0.005) than did group B. Among 727 patients, surveillance colonoscopy was performed within 6 months in 55.8% of patients and within 12 months in 77.8%. Group B had a significantly shorter interval of surveillance colonoscopy than did group A (P<0.001). There was no difference in detection of advanced neoplasia at surveillance colonoscopy between the 2 groups (6.6% vs. 5.4%, P=0.638). CONCLUSIONS: The recommended interval of surveillance colonoscopy is not followed in Korea. More education about post-polypectomy surveillance guidelines is required.