Background <p>Endoscopic retrograde cholangiopancreatography is the gold-standard treatment for malignant distal biliary obstruction. However, when endoscopic retrograde cholangiopancreatography cannot be successful, endoscopic ultrasound-guided rendezvous and endoscopic ultrasound-guided antegrade stenting can be performed as salvage. Nevertheless, endoscopic ultrasound-guided hepaticogastrostomy is widely performed in cases of inaccessible papilla due to duodenal obstruction, although only at high-volume centers owing to its technical challenges and the high risk of complications. There are some reports showing that initial percutaneous transhepatic biliary drainage before conversion to endoscopic ultrasound-guided hepaticogastrostomy can reduce the rate of adverse events; however, there are no case reports describing the conversion of percutaneous transhepatic gallbladder drainage to endoscopic ultrasound-guided hepaticogastrostomy combined with antegrade stenting.</p> Case presentation <p>We describe a case of successful conversion of percutaneous transhepatic gallbladder drainage to endoscopic ultrasound-guided hepaticogastrostomy combined with antegrade stenting for a malignant distal biliary obstruction caused by an invasive intraductal papillary mucinous carcinoma in an 82-year-old Japanese woman who was referred to our hospital with jaundice. Blood test results revealed increased levels of white blood cell counts and hepatobiliary enzymes. Abdominal contrast computed tomography disclosed a pancreatic tumor that caused the malignant distal biliary obstruction. The final diagnosis was invasive unresectable intraductal papillary mucinous carcinoma, and endoscopic retrograde cholangiopancreatography was not possible owing to severe duodenal stenosis caused by invasion of the intraductal papillary mucinous carcinoma. Despite the severe duodenal stenosis, there were no symptoms of gastric outlet obstruction. We performed percutaneous transhepatic gallbladder drainage for biliary drainage because percutaneous transhepatic biliary drainage was unsuccessful owing to insufficient dilation of intrahepatic bile ducts. Following successful percutaneous transhepatic gallbladder drainage, the patient’s symptoms resolved. After 2&#xa0;weeks, conversion of percutaneous transhepatic gallbladder drainage to endoscopic ultrasound-guided hepaticogastrostomy combined with antegrade stenting was performed. Contrast medium diluted with normal saline was injected through the percutaneous transhepatic gallbladder drainage catheter, and the expanded B2 intrahepatic bile duct was punctured using a 19-gauge needle under endoscopic ultrasound guidance. The guidewire was advanced beyond the biliary obstruction and major papilla. Finally, an uncovered metal stent was placed in an antegrade manner, and a dedicated plastic stent was placed across the hepaticogastrostomy tract without any complications. The patient showed a good clinical course and was subsequently discharged.</p> Conclusions <p>Although conversion of percutaneous transhepatic gallbladder drainage to endoscopic ultrasound-guided hepaticogastrostomy combined with antegrade stenting is feasible and safe, further studies are required to confirm the efficacy of this approach.</p>