BACKGROUND/AIMS: The discrepancy of the histopathological diagnosis between endoscopic forcep biopsy, surgery and endoscopic mucosal resection (EMR), has been reported on in a previous study. We compared the results of endoscopic forcep biopsy and the histopathologic diagnosis after performing endoscopic submucosal dissection (ESD). METHODS: We retrospectively reviewed 434 lesions for which we were able to compare the post-ESD histopathologic results with the endoscopic biopsy. RESULTS: 1) Of the 14 lesions that showed chronic gastritis or atypia by endoscopic biopsy, 9 were diagnosed with carcinoma in situ or adenocarcinoma after ESD. 2) fifty one of 141 lesions that showed low grade dysplasia on the endoscopic biopsy were diagnosed with carcinoma in situ or adenocarcinoma after ESD. 3) Of the 60 lesions that showed high grade dysplasia on the endoscopic biopsy, 46 were diagnosis with carcinoma in situ or adenocarcinoma after ESD. CONCLUSIONS: The discrepancy of the histopathological diagnosis was found between ESD and forcep biopsy. In light of these results, if a lesion that is suspected to be EGC, although it is not diagnosed by endoscopic biopsy, then it should be confirmed by ESD.