['Magnifying endoscopy with narrow-band imaging (ME-NBI) is more reliable than chromoendoscopy (CE) for delineating the horizontal extent of early gastric cancers prior to endoscopic submucosal dissection (ESD). However, the added benefits of ME-NBI over CE in terms of the difference in magnification level have yet to be elucidated. The aim of this study was to investigate the improvement in diagnostic accuracy for tumor delineation obtained with different magnification levels of ME-NBI following CE.', 'This was a retrospective study, performed at a single tertiary referral center. A series of 158 consecutive patients with 161 early gastric cancers resected en bloc using ESD was included in the study. The margins of each lesion were examined in their entirety using CE, followed by low power optical magnifying endoscopy with narrow-band imaging (LM-NBI), and finally the highest power optical magnifying endoscopy with narrow-band imaging (HM-NBI). The primary endpoint was the added benefit, as measured using the successful delineation rate, for the delineation of gastric cancer margins using CE\u2009+\u2009LM-NBI vs CE, and for CE\u2009+\u2009LM-NBI\u2009+\u2009HM-NBI vs CE\u2009+\u2009LM-NBI.', 'The successful delineation rates (95 % CI) using CE, CE\u2009+\u2009LM-NBI and CE\u2009+\u2009LM-NBI\u2009+\u2009HM-NBI were 72.7 % (68.5-79.9 %), 88.9 % (84.2-93.8 %), and 98.1 % (95.8-100 %). The diagnostic accuracy improved significantly for CE\u2009+\u2009LM-NBI compared with CE (P\u2009<\u20090.001), and for HM-NBI compared with LM-NBI (P\u2009<\u20090.001).'] Is highest power magnification with narrow-band imaging useful for improving diagnostic performance for endoscopic delineation of early gastric cancers?