Cardiopulmonary bypass has been widely used in the management of isolated single and double lung transplantations. Although there are certain clear- cut preoperative indications for cardiopulmonary bypass, in many patients the decision to use this modality is based on the hemodynamic consequences of intraoperative pulmonary artery clamping. We have performed 109 isolated lung transplantations. In 69 patients (38 single lung transplantations and 31 double lung transplantations) cardiopulmonary bypass was initiated only on the basis of intraoperative hemodynamics. We have analyzed preoperative data from these 69 patients to determine whether an intraoperative requirement for cardiopulmonary bypass can be predicted. Of 38 single lung transplantations, 12 necessitated cardiopulmonary bypass (all patients had restrictive lung disease). No patients with obstructive lung disease who underwent single lung transplantation required cardiopulmonary bypass (p < 0.001). For single lung transplantations, 6-minute walk, the arterial desaturation/oxygen requirements on exercise, and the right ventricular ejection fraction were all significantly different between the cardiopulmonary bypass and non- cardiopulmonary bypass groups (p < 0.001). Of 31 double lung transplantations, 10 patients required cardiopulmonary bypass (seven had bronchiectasis, two had obstructive lung disease, and one had restrictive lung disease). For obstructive lung disease, no preoperative parameters predicted cardiopulmonary bypass. In conclusion, cardiopulmonary bypass is not necessary for most patients undergoing lung transplantation (in the absence of an absolute preoperative indication). Obstructive lung disease rarely necessitates cardiopulmonary bypass. In single lung transplantations, the subsequent requirement for cardiopulmonary bypass can be predicted from preoperative cardiopulmonary performance. For double lung transplantations, the requirement for cardiopulmonary bypass is usually dependent on unpredictable intraoperative factors.