Peroral endoscopic myotomy (POEM) is effective for treating achalasia and associated disorders1, 2. However, mediastinitis is a severe adverse event that may occur after POEM because of contact between the esophageal lumen and mediastinum after inadequate mucostomy closure or mucosal injury in the early period after POEM. A 48-year-old man was admitted to our hospital with advanced sigmoid-type achalasia (Fig. 1a). Several balloon dilatations were unsuccessful; therefore, POEM was carried out (Fig. 1b). Because of chronic and severe esophagitis, the mucosa was extremely thick and hard. A longitudinal mucosectomy was done on the posterior side of the lower esophagus, and an 8-cm posterior myotomy was carried out. We finally attempted to close the mucostomy using a clip; however, it was extremely challenging because of the thickened mucosa. Therefore, the endoloop/clips technique was carried out in a purse-string manner to close the mucostomy using two endoscopes (Fig. 1c,d). First, the distal side of the mucostomy was fixed to the endoloop using a short clip. Second, the clips were placed at an equal distance from both the distal and proximal sides of the mucostomy. Finally, the mucostomy was closed in a purse-string manner. Postoperative endoscopic and barium swallow examinations revealed no leakage to the mediastinum. Maintaining a reliable mucostomy closure during POEM is crucial for preventing the leakage of esophageal contents into the mediastinal space. However, achalasia with a thickened mucosa as a result of chronic and severe esophagitis may have been countered. This was because of unsuccessful mucostomy closure by conventional procedures. Several endoscopic suturing techniques during POEM have presently been reported.3-5 Purse-string closure using the endoloop/clips technique is effective for a safe mucostomy closure, regardless of thickness or hardness, and does not require specialized instrumentation (Fig. 2; Video 1). This method can be carried out using either a single dual-channel endoscope or two endoscopes. The author wish to thank Dr. Kanefumi Yamashita, Dr.Toshihiro Ohmiya (Department of Gastroenterological Surgery, Faculty of Medicine, Fukuoka University) and all clinical staff for their contribution to this study. Authors declare no conflict of interests for this article. No financial support was received for this study. Additional Supporting information may be found in the online version of this article at the publisher's web site. Video S1 Endoloop/clips technique carried out in a purse-string manner (porcine model). First, the distal side of the mucostomy was fixed to the endoloop using a clip. Then, the clips were placed at an equal distance from both the distal and proximal sides of the mucostomy. Finally, the mucostomy was closed in a purse-string manner. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.