Advances in techniques of image diagnosis have enabled the detection of minute or small cancer lesions in the stomach. Patients with such cancer, in principle, were treated surgically, but accumulated histopathological data on surgical cancer specimens revealed that many of these patients did not have any metastatic lesions. For those localized cancers, local treatment of primary lesions by endoscopy gives curative results. It has been demonstrated that endoscopic therapy is curative in mucosal well-differentiated adenocarcinoma not more than 20 mm in diameter without ulceration. Efforts to cure early gastric cancer without surgery yielded fruitful results and a new treatment concept was established. Even if there is a recurrence of the residual or metachronous lesions, they can be treated by further endoscopic treatment.