BACKGROUND: Mucinous cystadenomas of the liver are rare cystic neoplasms. The aim of this study was to assess management of a consecutive series of patients who underwent laparotomy for a suspected cystadenoma or cystadenocarcinoma. Secondly, the origin of ovarian stroma (OS) in mucinous liver cystadenomas was examined during early embryonic development. PATIENTS AND METHODS: Patients diagnosed with mucinous liver cystadenomas or cystadenocarcinoma between 1994 and 2009 were included. Pathology specimens of patients who had undergone resection were reviewed for OS. Furthermore, in human embryos, morphology of the peritoneal epithelium and the position of the gonads in relation to the embryonic liver, pancreas and spleen were examined. RESULTS: 15 surgically treated patients (13 female, 2 male) with hepatic tumors were eventually diagnosed with mucinous liver cystadenomas (12) or cystadenocarcinomas (3). OS was present in all female patients with mucinous cystadenoma or cystadenocarcinoma. The 2 male patients were rediagnosed as intraductal papillary mucinous neoplasm (IPMN) or cystadenocarcinoma with features of IPMN. In human embryos, preceding their 'descent', the gonads are situated directly under the diaphragm, dorsal to the liver, the tail of the pancreas and the spleen, but separated from these organs by the peritoneal cavity. In contrast to the peritoneal epithelium elsewhere, the cells covering the gonads show an activated morphology. CONCLUSION: For the diagnosis of mucinous liver cystadenoma, the presence of OS is prerequisite. This may be explained by the common origin of cystadenoma and OS in epithelial cells that cover the embryonic gonads in early fetal life.