BACKGROUND. Post-operative chylous effusion is rare in infants. It may result from venous thrombosis, thoracic duct injury or lymphatic vessel obstruction. This paper describes 2 cases of diaphragm hernia with post-operative chylous effusion. CASE REPORTS Case 1: A newborn developed chylous ascites two weeks after repair of a left posterolateral diaphragm hernia. Abdominal paracentesis showed milky fluid containing numerous lymphocytes (98%). Ascites was rapidly reduced by feeding with medium-chain triglyceride-rich (MCT) formula. Case 2: A chylothorax was seen 7 days after surgery to repair a left posterolateral diaphragm hernia. Thoracocentesis showed serous fluid containing numerous lymphocytes (93%). The chylothorax was resolved after two thoracocenteses, parenteral nutrition and feeding with MCT formula. CONCLUSION. These cases are the third report of chylothorax and the second report of chylous ascites after surgical repair of a diaphragm hernia. The exact cause of the chylous effusion is not clear.