Microcystic cystadenoma of the pancreas is a well-recognized although rare pathological entity. All previously reported examples of this tumor have been uniformly benign in behavior. In this case report, we present a primary tumor of the pancreas that was histologically indistinguishable from microcystic adenoma, but which behaved in a malignant fashion. Metastases were found in the stomach and liver. We believe that this case represents a new entity, which we have termed "serous cystadenocarcinoma of the pancreas."