OBJECTIVE We wanted to assess the prevalence of pulmonary dysfunction as the underlying reason for inoperability among patients with non-small-cell lung cancer (NSCLC) who were considered for surgical treatment at the time of diagnosis. METHODS This is a retrospective analysis of all patients with NSCLC referred to our pulmonary function laboratory for preoperative evaluation between January 2001 and November 2001. Pulmonary function testing consisted of measurement of spirometric indices (forced expiratory volume in 1 second [FEV1]), lung volumes and diffusing capacity for carbon monoxide, Xenon-133 quantitative ventilation and perfusion studies, and exercise testing when indicated. Patient demographics and clinical characteristics at the time of the evaluation were reviewed. RESULTS The group comprised 206 consecutive potential surgical candidates (mean age, 64.7 years +/- 10.1 years) with NSCLC. Nearly half (45.6%) of the patients had early-stage (I/II) disease, and the remainder had late-stage disease at the time of pulmonary evaluation. The average predicted FEV1 among all patients was 70.3% +/- 19.6% (range, 25%-123%). One hundred eight patients (52.4%) were deemed surgically inoperable after the preoperative assessment. Severe pulmonary function impairment was identified as the reason for surgical inoperability in more than one third of these patients (40 of 108). CONCLUSIONS A substantial number of patients with anatomically resectable NSCLC are deemed surgically ineligible based on poor lung function. Recognition of the magnitude of this problem is fundamental to the development of effective treatment options, which might include preoperative management strategies that could better prepare patients for surgery or, alternatively, aggressive nonsurgical approaches.