Advances in operative technique and perioperative care have reduced surgical morbidity and mortality considerably after pulmonary resections. Various single and combined parameters of functional operability have been proposed to assess the surgical risk. Patients with normal or only slightly impaired pulmonary function (FEV1 and DLCO > or = 80% predicted) and no cardiovascular risk factors can undergo pulmonary resections up to a pneumonectomy without further investigation. For others, exercise testing, pulmonary split-function studies, or a combination of these methods are recommended. Cardiopulmonary exercise testing, most frequently performed as a symptom-limited test with the measurement of VO2max, assesses the pulmonary and cardiovascular reserves. A VO2max of less than 10 mL/kg/minute generally is considered prohibitive for any resection, a value of greater than 20 mL/kg/minute or greater than 75% predicted normal, safe for major resections. Split-function studies are radionuclide-based estimations of the ppo values of various parameters. The currently used ppo parameters are FEV1-ppo, DLCO-ppo, and VO2max-ppo. Suggested cutoff values for safe resection are: FEV1-ppo and DLCO-ppo 40% or greater than predicted, and V(r)O2max-ppo 35% or greater than predicted, combined with an absolute value of greater than or equal to 10 mL/kg/minute. The lowest acceptable ppo values remain to be confirmed by additional prospective studies. Resections involving not more than one lobe usually lead to an early functional deficit followed by recovery. The permanent loss in pulmonary function is small (approximately 10%) and exercise capacity is reduced only slightly or not at all. Pneumonectomy leads to an early permanent loss of about 33% in pulmonary function and approximately 20% in exercise capacity. Pulmonary function tests alone therefore overestimate the functional loss after lung resection.