The authors describe a case of giant benign cystadenoma of the ovary in a 55 year old woman. The patient came to their observation complaining of severe abdominal pain which started right after she was treated with a paracentesis, because of the suspicion of cirrhosis with ascites. The authors briefly outline the two goals of the diagnostic strategy: the diagnosis of the disease and the diagnosis of the nature of the disease. They stress the utmost importance of ultrasound and computerized tomography scans in the diagnosis of disease. For the diagnosis of the nature of the disease the authors counted on Ca 125, CEA, LDH levels and on Ca 19.9 and ACE levels as well. The surgical management of abdominal mass, which is the only possible treatment, led to the removal of a 60 cm in diameter and 30 kg mucinous cystadenoma. After the viscera of the higher abdomen (liver and stomach) had been repositioned, a plastic closure of the enormously expanded anterior abdominal walls was performed.