An annular pancreas is a rare malformation. It is generally accepted that the ring formation originates from a single ventral pancreas, as suggested by Lecco. No reports of resected and/or autopsied annular pancreata derived from paired ventral pancreata, thus supporting Baldwin's hypothesis, have been published. We describe an annular pancreas originating from paired ventral pancreata, thus supporting Baldwin's hypothesis, and attempt to clarify the pathogenesis of an annular pancreas. The patient was a 1-day-old Japanese male newborn, born at 32 weeks of pregnancy. He died from respiratory failure owing to esophageal atresia the next day. Autopsy incidentally revealed an annular pancreas that was examined histologically. Multiple 4 microm thick serial sections were obtained from paraffin-embedded pancreatic tissue. Sections for histologic analysis were subjected to hematoxylin-eosin staining and pancreatic polypeptide immunostaining. An unusually large pancreatic duct encircled by pancreatic tissue ran around the duodenum, and the duct was confirmed to flow into the major papilla. The islets of the encircling pancreas were positive for pancreatic polypeptide. A normal main and accessory pancreatic duct were also identified. Histologic and immunohistochemical evaluation revealed that the ring formation originated from the left lobe of paired ventral pancreata. An annular pancreas that was investigated histopathologically and immunohistochemically and found to support Baldwin's hypothesis is described.