Chylothorax is a rare but serious complication of coronary artery bypass grafting. We describe a case of double myocardial revascularization with the internal mammary artery developing the complication ten weeks after cardiac surgery. The reasons for late symptomatology of lymphatic injury are analyzed. Conservative treatment with low-fat diet, total parenteral nutrition and pleural drainage was attempted unsuccessfully; chyle leakage of around 500 ml/day and onset of nutritional deficiency made it advisable to seal the thoracic duct surgically.