- Mesenteric cyst is a rare, benign lesion. A 59-year-old woman was admitted with abdominal distension. Physical examination and abdominal ultrasound indicated remarkable ascites. Aspiration revealed a clear transudate and computerized tomography showed a giant mesenteric cyst. At operation the cyst was removed. Giant mesenteric cysts can mimic ascites. This diagnosis should be included in the differential diagnosis of abdominal distension, even when ultrasound examination indicates ascites.