Twenty one patients with the pancreatic cyst on whom operation was given in our department from 1965 to 1984 were divided into those with the inflammatory cyst (16 cases) and with the neoplastic cyst (5 cases), and the surgical results were examined. The surgical formulas of the inflammatory cyst were further divided into 9 cases of internal drainage of the cyst into the gastrointestinal tract, 1 case of external drainage, and 6 cases of cyst excision together with the resection of the pancreas, and the results were rather satisfactory. On the other hand, the cases of the neoplastic cyst were divided into 2 cases of cystadenocarcinoma, 1 case of cystadenoma and 2 cases of mucinous adenocarcinoma. The contents in the cyst were all mucinous. It is considered that, when the contents of the pancreatic cyst are mucinous, its malignant potential is high. Since examination during operation is often insufficient, we have been trying to recommend resection so far as possible.