A 58-year-old Japanese man had tarry stool and severe anemia. Neither upper nor lower gastrointestinal (GI) endoscopy showed any localized lesions. Thus, the source of his GI bleeding was suspected to be in the small intestine, and he underwent peroral double-balloon enteroscopy (DBE) using EN-450T5 (Fujinon-Toshiba ES System Co., Tokyo, Japan). There were no lesions considered to be the source of GI bleeding. After the procedure, the patient began to experience abdominal pain. Laboratory tests revealed hyperamylasemia and abdominal computed tomography revealed an inflammation of the pancreas and the peripancreas. He was thus diagnosed to have acute pancreatitis. Conservative treatments resulted in both clinical and laboratory amelioration. He had no history of alcohol ingestion, gallstone disease or pancreatitis. Magnetic resonance cholangio-pancreatography demonstrated no structural alterations and no stones in the pancreatobiliary ductal system. As his abdominal pain started after the procedure, his acute pancreatitis was thus thought to have been related to the peroral DBE. This is the first reported case of acute pancreatitis probably associated with peroral DBE. A 58-year-old Japanese man had tarry stool and severe anemia. Neither upper nor lower gastrointestinal (GI) endoscopy showed any localized lesions. Thus, the source of his GI bleeding was considered to be in the small intestine, and he underwent peroral There are no tumors considered to be the source of GI bleeding. After the procedure, the patient began to experience abdominal pain. Laboratory tests revealed hyperamylasemia and abdominal computed tomography revealed an inflammation of the pancreas and the peripancreas. He was thus diagnosed to have acute pancreatitis. He had thus history of alcohol ingestion, gallstone disease or pancreatitis. Magnetic resonance cholangio-pancreatography demonstrated no structural alterations and no stones in the pancreatobiliary ductal system. As his abdominal pain started after t he procedure, his acute pancreatitis was thus thought to have been related to the peroral DBE. This is the first reported case of acute pancreatitis probably associated with peroral DBE.