Agenesis of dorsal pancreas is a rare congenital anomaly that arises from the failure of the dorsal pancreatic bud of endodermal cells to form the body and tail of the pancreas. It may be associated with diabetes mellitus, pancreatic exocrine dysfunction, or abdominal pain. Complete or partial agenesis of dorsal pancreas has been reported in a small number of pediatric and adult patients. A case is herein described involving a complete agenesis of dorsal pancreas and diabetes mellitus. A 38-year-old man with a 7-months history of non-insulin dependent diabetes mellitus was admitted due to weight loss and abdominal pain. Abdominal ultrasonography and computed tomography showed a normal biliary tree and enlarged head of the pancreas without visualization of the pancreatic body and tail. Endoscopic retrograde cholangiopancreatography (ERCP) revealved the short duct of Wirsung in the uncinate process and a head without opacification of any ducts in the pancreatic body or tail. The patient underwent explo-laparotomy for evaluation of the suspected pancreatic cancer. The patient was diagnosed as having complete agenesis of the dorsal pancreas by ERCP, CT, and surgery.