Background and Aims: Endoscopic resection (ER) of superficial adenocarcinoma of the esophagogastric junction (AEGJ) has been shown to be safe and effective. However, long-term data in patients undergoing ER for superficial AEGJ in Japan are still limited. The aim of this study was to determine the effect of ER on survival and occurrence of metachronous cancer of patients with superficial AEGJ. Methods: A retrospective analysis of patients who underwent or endoscopic submucosal dissection (ESD) for superficial AEJG in 13 centers in Japan was performed. The patients were classified as either low risk or high risk for lymph node metastasis based on histologic features. The incidence of metachronous AEGJ as well as overall survival and disease-specific survival rates were calculated. Results: A total of 372 patients who underwent ER were included, in which 277 patients were low risk and 95 high risk for lymph node metastasis. Five-year cumulative incidences of local recurrence were 13% and .5% in the EMR and ESD groups, respectively (P < .01). Six AEGJ deaths were observed in the high-risk group and none in the low-risk group. The 5-year overall survival rates in the low-risk group without additional treatment, the high-risk group with additional treatment, and the high-risk group without additional treatment were 93.9%, 77.7%, and 81.6%, respectively. The 5-year disease-specific survival rates in the 3 groups were 100%, 94.4%, and 92.8%, respectively. The 5-year cumulative incidence of metachronous AEGJ in 316 patients without additional treatment was 1.1%. Conclusions: Favorable long-term outcomes with ER were observed in patients with AEGJ who met the low-risk criteria for lymph node metastasis. ESD was a reasonable and effective treatment in Japanese patients.