We present a case of a 53-year old male patient who underwent elective surgery due to a giant abdominal cystic mass. Prior to the surgery, he complained of abdominal distention, growing abdominal mass and increasing nourishment problems. CT and ultrasonographic examinations revealed a giant abdominal cyst but failed to indicate the point of its origin. Intraoperatively a giant abdominal cyst was found, approximately 30x30x25 cm in size. The cyst was free-lying in the peritoneal cavity, except small area adherent to the stomach wall. Partial resection of the stomach wall was performed and the cyst was completely removed.The postoperative course was uncomplicated. The pathological examination did not give an unequivocal answer as to the origin of the cyst, suggesting differentiation between a tumor of vascular origin and of stromal origin.