We report the case of a 42-year-old man with a large pancreatic pseudocyst, the presence of which was not suspected upon initial presentation. This case provides an example of when imaging may be useful for the detection of pancreatitis and its complications. It also demonstrates classic pseudocyst localization to the lesser sac and left anterior pararenal space. The unusually large size of this pseudocyst provides a clear delineation of retroperitoneal fascial planes and an illustration of possible clinical consequences of mechanical obstruction by pseudocyst.