Ultrasonography is the method of choice in the diagnosis of ovarian cysts. In this case report, a cyst of enormous volume (>35 litres) was limiting the application of ultrasound techniques giving the false impression of ascites. A 55-year-old woman was finally diagnosed as having a giant ovarian mucosal-serosal cystadenoma of borderline potential after undergoing a total abdominal hysterectomy with salpingo-oophorectomy and excision of the cyst. In the literature, similar conditions have been described with the term 'empty abdomen'.