A 31-year-old woman with epigastric pain was given a diagnosis of a pseudocyst associated with pancreatitis. Despite treatment, symptoms did not completely improve and she was referred to our hospital. Since imaging examinations demonstrated findings characteristic of mucinous cystic neoplasm, the lesion was resected. Histopathologic examinations revealed mucinous cystic adenoma. Remains of intracystic hemorrhage were evident and short-term morphological changes were presumed to be associated with hemorrhage.