The most common pancreatic cystic lesion is pancreatic pseudocyst which represents about 85%. Primary cystic neoplasms represent about 10 to 15% of the lesion. Pathologically cystic neoplasms can be classified into serous cystadenoma, mucinous cystadenoma and papillary cystic neoplasm by epithelial lining-cell, whereas pseudocyst is characterized by fibrotic capsules. Mucinous form is known to be premalignant or malignant and serous cystadenoma was known to be benign in the past, but recently 4 cases of malignant transformation have been reported. Serous cystadenoma is described under a variety of names, including microcystic adenoma and glycogen-rich cystadenoma but recently macroqystic variants have been reported. Serous cystadenoma is most commonly seen in middle aged women with symptoms of vague upper abdominal pain or palpable mass. It is sometimes associated with extra- pancreatic diseases such as gallstones, diabetes mellitus, hypertension, duodenal ulcers, sterility, obesity and thymic dysfunction, but coexisting papillary thyroid cancer have been reported in only 2 cases to our knowledge. The pathogenesis of associated diseases is unknown and appears to be due to function of age of the patients or incidental occurrence. Herein, we report a patient who had a pancreatic serous cystadenoma coexisting with papillary thyroid cancer. Since pancreatic serous cystadenoma can occur in association with papaillary thyroid cancer, examination of thyroid seems to be advisable when pancreatic serous cystadenoma is found.