We report a successful endoscopic ultrasonographyguided drainage of a huge infected multilocular walledoff necrosis(WON) that was treated by a modified single transluminal gateway transcystic multiple drainage(SGTMD) technique. After placing a widecaliber fully covered metal stent, follow-up computed tomography revealed an undrained subcavity of WON. A large fistula that was created by the wide-caliber metal stent enabled the insertion of a forward-viewing upper endoscope directly into the main cavity, and the narrow connection route within the main cavity to the subcavity was identified with a direct view, leading to the successful drainage of the subcavity. This modified SGTMD technique appears to be useful for seeking connection routes between subcavities of WON in some cases. We report a successful endoscopic ultrasonographyguided drainage of a huge infected multilocular walledoff necrosis (WON) that was treated by a modified single transluminal gateway transcystic multiple drainage (SGTMD) technique. After placing a widecaliber fully covered metal stent, follow-up computed tomography revealed an undrained subcavity of WON. A large fistula that was created by the wide-caliber metal stent enabled the insertion of a forward-viewing upper endoscope directly into the main cavity, and the narrow connection route within the main cavity to the subcavity was identified with a direct view, leading to the successful drainage of the subcavity. This modified SGTMD technique appears to be useful for seeking connection routes between subcavities of WON in some cases.