Recent improvements in endoscopic techniques and technologies and an increased understanding and recognition of the importance of early gastric cancer (EGC) will result in increases in the detection and diagnosis of precancerous or early cancerous lesions. The incidences of nodal metastasis of intramucosal and submucosal EGC are 3 and 20%, respectively. Therefore, major surgery may be inappropriate in many of these patients, and many cases of EGC may be treated by endoscopic mucosal resection (EMR). EMR was first introduced in Japan 20 years ago. Most EMR have been performed by the so-called ‘strip biopsy’ or EMR-C methods. However, we have sometimes experienced local recurrence in cases that had been resected in multiple fragments by these methods. To obtain ‘complete resection’, we developed the endoscopic submucosal dissection (ESD) technique using a special endoscopic knife, the insulation-tipped diathermic knife (IT knife). The rate of complete resection, i.e. cut margin free from cancer and one-piece resection, was remarkably higher for the IT knife technique than conventional EMR. ESD cases are increasing rapidly in Japan. EMR including ESD is a good method for patients with gastric cancer to preserve the stomach. For EMR, it is necessary to find EGC. Both diagnosis and treatment are important, and scientific data regarding lymph node metastasis and clinicopathological features are required.