Serous cystadenomas of the pancreas have been classified as benign exocrine tumors. There have been rare cases of malignant behavior, and in exceptional cases, coexisting neoplasms have been reported. We report a case of a coexistent neuroendocrine tumor identified within a serous cystadenoma in a 78-year-old woman, which was discovered incidentally after complete resection of the tumor. Given the unpredictable metastatic potential of neuroendocrine tumors of the pancreas, we advocate complete resection of all pancreatic cystic tumors, combined with careful sampling of the pathological specimen to rule out a coexistent potentially malignant neoplasm.