Cystadenomas occur rather rarely among the cystic lesions of the pancreas, but they nevertheless require special attention. These cystadenomas do have a tendency for malignant degeneration, especially their mucinous form with papillary proliferation of the epithelium; insofar cystadenomas have to distinguished from retention nor pseudocysts, resulting from pancreatitis or from traumatic lesions of the pancreas. Differentiation of cystadenomas and other cysts can neither be achieved by preoperative diagnostic procedures nor by macroscopic findings during surgery. Diagnosis however can be established after biopsy during surgery. A cystadenoma has to be suspected especially in women of middle age, who do not have any history of pancreatitis, abdominal trauma or alcoholism, if the lesion is localized in the corpus or tail are of the pancreas. Cystadenoma have to be treated as potentially malignant tumors. The therapy of choice is excision far out in normal tissue; this is the only way to prevent relapses and to avoid transition of the lesion into a carcinoma. Thus, it has to be postulated for all patients who are being operated upon because of cysts of the pancreas that multiple biopsies should be done from various parts of the cystic wall during surgery and that drainage of the cyst should be performed only if a cystadenoma can be excluded.