Although use of the internal thoracic artery (ITA) for coronary artery bypass grafting results in superior graft patency and improved patient survival, our initial clinical observations suggested an increased incidence of pleuropulmonary morbidity with its use. One hundred consecutive patients with left ITA grafts were studied prospectively and compared with a consecutive retrospective group of 100 patients undergoing coronary artery bypass grafting with saphenous vein grafts only. Preoperative, postoperative day (POD) 2, POD 6, and postoperative week 8 chest roentgenograms were analyzed for atelectasis and effusion. Postoperative left lower lobe atelectasis was common in both groups on both POD 2 (saphenous vein, 43%, versus ITA, 53%; not significant) and POD 6 (saphenous vein, 40%, versus ITA, 41%; not significant). There was a significantly higher incidence of pleural effusion on POD 6 in the ITA group (84% versus 47%; p less than 0.05) but most of these were small. There was more chest tube drainage (1,413 versus 1,028 mL; p less than 0.01) and a greater need for secondary thoracostomy or thoracentesis (4% versus 0%) in the ITA group. The left pleural space was opened in 67 of the 100 ITA patients but pleurotomy did not appear to influence postoperative morbidity. We conclude that use of the internal thoracic artery for coronary artery bypass grafting results in a small but significant increase in pleuropulmonary morbidity.