An adult case of cystic lymphangioma in mesentery of the jejunum presenting with acute abdomen is reported. A 54-year-old woman was admitted to our hospital because of sudden upper abdominal pain and fever. On admission, slight inflammation and liver dysfunction were found. Abdominal ultrasonography
revealed two irregular cystic tumors at the epigastrium. The cystic tumors with septal structure and relatively strong internal echo were surrounded by unclear strong marginal echo. Three days after admission, when symptoms had been improved by antibiotics, the cystic tumors had reduced in size, becoming more flat with clear margin. The septal structure and the internal echo had diminished as well, though they remained persistent and faint. After CT, GI tract examination, angiography, MRI and ultrasonography, a diagnosis was made of infected mesenteric cysts of the jejunum. Surgery was performed, two tumors were found in the mesentery of the jejunum, and excised en bloc. A large cyst was situated in the center of the larger tumor, and a solid part at the right side of the cystic tumor was found. Histologic findings of the solid part indicated cystic lymphangioma with inflammation and hemorrhage.