A 57-year-old man was admitted to our hospital with adhesive bowel obstruction following pancreaticoduodenectomy performed for cholangiocarcinoma 4 months earlier. After admission, the patient remained nil per os and was closely observed. On the third day of admission, he developed worsening abdominal pain, and computed tomography revealed strangulation of the small intestinal mesentery dorsal to the superior mesenteric artery, with prolapse of the small intestine into the right upper quadrant to form a closed loop. Strangulated bowel obstruction secondary to internal hernia was diagnosed, and he underwent emergency surgery. Intraoperatively, we detected a hernia orifice formed by the mesentery and peritoneum at the site of the defect following resection of the ligament of Treitz, and we observed that approximately 2 m of the small intestine had prolapsed into the right upper quadrant. The herniated intestine was returned to the abdominal cavity, and the hernia orifice was sutured following hernia reduction. Few reports have described an internal hernia after pancreaticoduodenectomy; however, it has been reported that this operation can result in various types of internal hernia because of the complicated reconstructive procedure. Here we report our findings in this unique case together with a literature review.