We reviewed the management of 25 cases of chylothorax/chylopericardium (CT/CP) in 24 patients (9 females, 15 male; 3 days to 11-years-old) following 1605 cardiothoracic procedures (incidence of 1.5%) between January 1984 and December 1993 at our institution. The surgical procedures preceding the occurrence of lymph leak included ligation of patent ductus arteriosus (6 patients), coarctation/double aortic arch repairs (3), complex intracardiac repairs (11), and systemic to pulmonary shunts (5). There were 3 CPs and 22 CTs. All of the patients were initially treated nonsurgically with diet modification using either total parenteral nutrition (TPN) or enteral low fat solid food or enteral elemental diet supplemented with intravenous lipid emulsion. Twenty-one cases (84%) responded to conservative therapy. Of those, 15 had TPN as the initial treatment; the average duration of lymph leak was 13.7 (range 7 to 30) days and the average maximal lymph leak was 39.4 (range 15 to 130) mL/kg per day. The other six cases had low-fat enteral diet as the initial treatment, four resolved completely. Two with high-central venous pressure had to be switched to TPN prior to complete resolution. The average duration of lymph leak in this subgroup was 30 (range 12 to 56) days with the average maximal lymph leak was 30.1 (range 8.5 to 59) mL/kg per day. Excluding these two cases, the average lymph leak of the rest of the group was very compatible to the TPN group of 15 days. Lymphocytopenia and hyponatremia were frequently seen during CT/CP (47.6% and 43%, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)