The British Thoracic Society and American College of Chest Physician guidelines outline criteria for investigating patients for lung cancer surgery. However, the guidelines are based on relatively old studies. Therefore, the relationship between pulmonary function test results and surgical outcome were studied prospectively in a large cohort of lung cancer patients.From January 2001 to December 2003, 110 patients underwent surgery for lung cancer. All underwent full lung function testing in order to predict post-operative lung function.The hospital mortality rate was 3% and major complication rate 22%. There was poor overall outcome in 13%. Mean pre-operative lung function values were: forced expiratory volume in one second (FEV1) 2.0 L (79.4% of the predicted value), and carbon monoxide diffusing capacity of the lung (DL,CO) 73.6% pred. The mean post-operative lung function values were: FEV1 1.4 L (55.6% pred), and DL,CO 51.3% pred. All lung function values were better predictors of poor surgical outcome when expressed as a percentage of the predicted value. Using a threshold of preoperative FEV1 of 47% pred resulted in the most useful positive and negative predictive probabilities, 0.90 and 0.67, respectively.Lung function values expressed as a percentage of the predicted value are more useful predictors of post-operative outcome than absolute values. The threshold of predicted forced expiratory volume in one second for surgical intervention could be lower (45-50% pred) than is currently accepted without increased mortality.KEYWORDS: Lung carcinoma, lung function, lung function tests, surgical resection S urgical resection remains the treatment of choice for anatomically resectable nonsmall cell lung cancer [1,2], offering the best prospect of long-term survival. However, many patients have coexisting chronic airflow limitation [3], which is associated with an increased risk from surgery. Loss of lung tissue may grossly impair post-operative ventilatory function in such patients, predisposing to cardiopulmonary complications, including death. The British Thoracic Society (BTS) and American College of Chest Physician guidelines [4,5] outline criteria for investigating patients with borderline lung function. However, many of the studies on which the guidelines are based are relatively old, and often based on predominantly male patients who were significantly younger than patients currently being considered for surgery.The latest BTS guidelines suggest that further investigation is unnecessary if a patient has a forced expiratory volume in one second (FEV1) of .2.0 L for pneumonectomy or .1.5 L for lobectomy. This is because studies have shown a mortality rate of ,5% using these criteria. However, these figures are based mainly on studies involving males, and it is likely that lower values would be more appropriate for females. It is possible that a figure based on a value expressed as a percentage of the predicted value would be better still, since this would also take into account the patient's age, s...