Accurate endoscopic diagnosis of gastric cancer invasion depth is essential in making a proper treatment strategy decision. We investigated the accuracy of diagnostic depth invasion in 1846 gastric cancers resected by surgery or endoscopy from 2001 to 2003 at our hospital. Diagnostic accuracy was 95% for early cancer and 86% for advanced cancer; and 85% for mucosal cancer and 46% for submucosal cancer. The rate of diagnostic inaccuracy was significantly higher in IIa+IIc type than in other macroscopic types; and lesions with UL than without UL; lesions >20 mm and those < or = 20 mm; as well as in undifferentiated type than in differentiated type, respectively. Endoscopic diagnosis of gastric cancer invasion depth was not always accurate and improved diagnosis for submucosal cancer in particular is necessary.