Seven cases of pancreatic cystadenocarcinoma were studied clinicopathologically and immunohistochemically. Four patients died of the disease or recurrence with metastasis to the liver and peritoneum within 2 yr after surgery. The remaining three patients are well after surgery. To distinguish the cystoadenocarcinoma with excellent prognosis from that with poor prognosis, we performed immunohistochemical staining with monoclonal antibodies directed against tumor markers. Five specimens were strongly and diffusely reactive with tumor marker antibodies, whereas two were reactive with the apical portion of lining epithelial cells. With the findings of the immunohistochemical examination, the diagnosis of two patients could be revised from cystadenocarcinoma to premalignancy. Thus, immunohistochemical examination with tumor markers could correlate with the clinical outcome of the patients and is useful in distinguishing two distinct populations of mucinous cystic tumor.