We report a case report of 51-years old woman, who was observed and regularly checked for slowly growing cystic expansion along right hepatic lobe for many years. On the basis of epidemiology history and picture (on ultrasonography, CT and MRI), the mass was considered to be subcapsular liver cyst of echinococcal origin. After 10 years from the first manifestation of clinical symptoms, size progression of the mass and dissemination into the peritoneum was found. It was followed by diagnostic laparoscopy, which revealed that the cystic mass wasn´t located inside the hepatic parenchym. The mass was located outside the liver, caused an impression of right liver lobe and adhered to the diaphragm. The result of biopsy demonstrated mucinous peritoneal metastasis of unknown primary origin. Due to the histological conclusion and retrospective evaluation of imaging methods we suppose it could be pseudomyxoma peritonei.