Two adult patients, a woman aged 36 and a man aged 29, were referred to the outpatient clinic with abdominal symptoms. They both had an uneventful medical history. The first patient had progressive pain in her back and physical examination revealed a palpable tumour in her abdomen. The second patient had had an altered defecation pattern for some time, but on physical examination no tumour was palpable in the abdomen. Ultrasound and CT examination of both patients showed a large cystic mass in the abdomen. During surgery, a large fixed cyst originating in the root of the mesentery was found in both patients, and radical resection was carried out. Histopathological examination revealed an intra-abdominal cystic lymphangioma. No recurrence was seen at follow-up. Intra-abdominal lymphangiomas are rare benign cystic tumours. Lymphangiomas occur at all ages, although they are mostly seen before the fifth year of life. Lymphangiomas are mostly found in the neck and axilla. Their exact aetiology is unknown, although some believe that it is associated with developmental anomalies of the lymphatic system. Most intra-abdominal lymphangiomas are asymptomatic, although some may present with acute symptoms. Radical surgical resection is the best treatment.