Over a period of 22 years, chylothorax developed in 9 of 1,800 patients who underwent pneumonectomy. Two groups were identified. In group I (n = 5), accelerated opacification of the pneumonectomy space was noted, but the mediastinum remained shifted to the pneumonectomy site. No hemodynamic problems developed and their course was no different from that of other patients who had undergone pneumonectomy. In the second group (group II; n = 4), rapid opacification of the pneumonectomy space was accompanied by mediastinal shift away from the pneumonectomy site and by major hemodynamic and respiratory embarrassment. All 4 patients required surgical intervention to control the chylous leak.