Complete excision of diffuse abdominal lymphangiomatosis in the newborn is next to impossible. A 3-day-old female infant was found to have diffuse abdominal lymphangiomatosis predominantly in the left mesocolon and retroperitoneum. Initial management was by marsupialization, which was complicated by chylous ascites requiring periodic paracentesis and nutritional support. At the age of 45 days, left hemicolectomy and partial excision of the retroperitoneal cysts were performed together with intracystic injection of OK-432 into the residual cysts. The patient's progress after the second operation was satisfactory. Initial marsupialization followed by delayed partial resection together with injection of OK-432 into the residual cysts is an effective method of managing diffuse abdominal lymphangiomatosis in the newborn.