Omental and mesenteric cysts are both rare pathologies in children. Children who have omental cysts usually display symptoms of abdominal distension, with or without a palpable mass. The mass can simulate ascites on clinical observation, or tuberculosis on radiological images. The optimal treatment for this condition is complete resection. The presenting symptoms of abdominal distension and the simulation of septated ascites and abdominal tuberculosis are unusual. Reported cases in the literature usually display symptoms of abdominal distension, abdominal pain, painless mass or possible ascites. We describe the clinical presentation of a five-and-a-half-year-old boy who was treated for a diagnosis of abdominal tuberculosis and ascites at another hospital. After three years, he underwent abdominal surgery, and an omental cyst was found intraoperatively. The diagnosis was confirmed by pathological examination.