Annular pancreas is a developmental anomaly of the pancreas. There are two major hypotheses concerning development of the annular pancreas from the ventral pancreatic anlage; adhesion of the right ventral anlage to the duodenal wall (Lecco's theory), and persistence of the left ventral anlage (Baldwin's theory) reported in 1910, but each theory has some problems and can account for only a few types of annular pancreas. We report a new embryologic hypothesis of annular pancreas which can account for the developmental mechanism of three types of arrangement of annular ducts. The tip of the left ventral anlage adheres to the duodenum and stretches to form a ring. Whether the tip is proximal or distal to the bile duct creates several arrangements of the annular duct.