AIM: To evaluate the determination of the margin of differentiated-type early gastric cancers by using conventional endoscopy.METHODS: We retrospectively evaluated 364 differentiated early gastric cancers that were endoscopically resected as en-bloc specimens and diagnosed pathologically in detail between November 2007 and October 2008. All procedures were done with conventional endoscopes and all endoscopic samples, before and after indigo carmine dye, were re-evaluated using a digital filing system by one endoscopist. We analyzed the incidence of lesions with unclear margins and the relationship between unclear margins and relevant clinicopathological findings. RESULTS: The rate of lesions with unclear margins was 20.6%(75/364). Multivariate regression analysis suggested that the factors that make the determination of the margin difficult were normal color, presence of components of flat area(0-IIb), a diameter ≥ 21 mm, ulceration, and components of poorly differentiated adenocarcinoma in the mucosal surface.CONCLUSION: As many as 20% of differentiated early gastric cancers show unclear margins. Consideration of the factors associated with unclear margins may help endoscopists to accurately determine the margins of the lesion. AIM: To evaluate the determination of the margin of differentiated-type early gastric cancers by using conventional endoscopy. METHODS: We retrospectively evaluated 364 differentiated early gastric cancers that were endoscopically resected as en-bloc specimens and diagnosed pathologically in detail between November 2007 and October 2008. All procedures were done with conventional endoscopes and all endoscopic samples, before and after indigo carmine dye, were re-evaluated using a digital filing system by one endoscopist. We analyzed the incidence of lesions with unclear margins and the relationship between unclear margins and relevant clinicopathological findings. RESULTS: The rate of lesions with unclear margins was 20.6% (75/364). Multivariate regression analysis suggested that the factors that make the determination of the margin difficult were normal color, presence of components of flat area (0- IIb), a diameter ≥ 21 mm, ulceration, and components of poorly differentiated adenocarci noma in the mucosal surface. CONCLUSION: As many as 20% of differentiated early gastric cancers show unclear margins. Consideration of the factors associated with unclear margins may help endoscopists to accurately determine the margins of the lesion.