Among the cystic lesions of the pancreas, pseudocysts are most common. This article summarizes the current state of knowledge on the morphology and pathogenesis of pseudocysts. Specifically, the pathogenetic relationship between pancreatic pseudocysts and acute and chronic pancreatitis and the natural history of pseudocysts will be discussed. In addition, this article gives a brief description of a few non-neoplastic pancreatic cysts, including retention cysts, congenital cysts, cystic acinar transformation, para-ampullary duodenal wall cysts, enterogenous cysts, endometrial cysts, and parasitic cysts.