A case of giant omental cyst diagnosed preoperatively is described. A 4-year old girl presenting with abdominal distension and misdiagnosed as having ascites, was subsequently proved to have a giant omental cyst. This is a rather difficult diagnosis to reach and results in wrong treatment methods. A high index of suspicion is therefore required early in the course of the disorder to decrease the complication rate. This report describes the diagnostic modalities and our approach to the patient who was cured by total excision of the cyst and free of disease in the fourth year of follow-up.