Chyloperitoneum is an extremely rare complication of abdominal surgery in children and a combined occurrence of chylothorax and chyloperitoneum after abdominal surgery has never been reported in children. Chylous ascites usually occurs as a result of operative trauma to the thoracic duct, cisterna chyli, or its tributaries. About one third of all patients with chylous ascites after retroperitoneal lymph node dissection also develop secondary chylothorax. Diaphragmatic defects have been shown to be responsible for the occurrence of chylothorax secondary to chyloperitoneum. Congenital diaphragmatic weakness may result in evagination of the peritoneum causing diaphragmatic blebs, the rupture of which results in the movement of the peritoneal fluid into the pleural cavity. In the authors' patient, the rent in the diaphragm that occurred during surgery was probably responsible for the chylothorax. The role of chemotherapy, if any, in the pathophysiology of this complication is unknown. Total parenteral nutrition (TPN) is a simple and effective treatment for postoperative chylous effusions. Surgical treatments such as abdominal exploration for the repair of leaking lymphatics and peritoneovenous shunt should be reserved for patients who fail TPN.