The authors present a 25-year-old female patient who underwent laparotomy for emergent indications due to acute peritonitis in the course of septic cystic transverse mesocolonic lymphangioma. Such a lesion can be classified as a benign neoplasm or as a congenital anomaly. These tumours are more prevalent in children, with a male preponderance. They are most commonly located within soft tissues of the neck. Peritoneal cavity involvement is less then 5%. Then, small bowel mesentery or mesocolon are the most frequently affected sites of the abdominal cavity. Chronic, partial intestinal obstruction is a major clinical manifestation of mesenteric lymphangioma. Acute abdomen presentation of the disease is uncommon and it can be caused by haemorrhage, perforation or torsion of a cyst or infection. The optimal treatment is radical excision of the lesion.