Approximately half the clinical diagnoses of pancreatic pseudocysts will be erroneous if made during the acute phase of coexisting pancreatitis. Since self-limiting peripancreatic edema may clinically simulate pseudocyst, previous natural history information is subject to question. Occasional spontaneous resolution of a pseudocyst has been confirmed in five patients using serial ultrasound studies. It appears that although most pseudocysts maintain dimensional stability, a few may exhibit relatively rapid changes in volume. The pathophysiologic and surgical implications of these observations are discussed.