The occurrence of pulmonary oedema was studied retrospectively in 243 patients who underwent pneumonectomy in one hospital from 1975 to 1984. Pulmonary oedema developed in eight of 113 patients who had a right sided pneumonectomy and in three of 130 patients undergoing a left sided procedure. It occurred more commonly in patients requiring a second thoracotomy because of blood loss (in three out of seven patients). There were no significant differences preoperatively in pulmonary function, lung perfusion scans, or cardiovascular condition between patients who subsequently developed pulmonary oedema and those who did not. Postoperative fluid balance was significantly more positive in patients developing pulmonary oedema than in those not developing oedema. Thus pulmonary oedema was associated with right sided pneumonectomy, repeat thoracotomy, and more positive fluid balance.