Pulmonary metastasectomy is an accepted procedure for treating selected patients with various stage IV malignancies. There is widespread consensus that lung-sparing local excisions should be performed instead of lobectomies whenever possible. For safety, a distance of 0.5 to 1 cm around the lesion is recommended in pulmonary metastasectomies.1 The most important prognostic factors, including histology, disease-free interval, completeness of resection, and number of metastases, are well described,2,3 but little is known about the effects of metastasectomy on lung function. The accepted criteria for selecting patients for pulmonary metastasectomy include those having completely resectable lesions in the lung, no evidence of metastases in other organs, sufficient pulmonary function, and no contraindications due to concomitant disease. Although imagining a complete tumor resection and calculating the anticipated amount of lung to be resected is a minor problem for experienced thoracic surgeons, the prediction of postoperative lung function is difficult, especially when multiple wedge resections or a combination of wedge resections and anatomic resections are planned. In lung cancer cases, prediction of postoperative pulmonary function using a simple formula based on the number of resected bronchopulmonary segments proved to be useful in identifying patients at increased risk of medical complications.4 A predicted postoperative (ppo) FEV1 of > 800 mL, or > 40% of the predicted FEV1, is a common selection criterion for resection candidates.5 To preserve this lowest desirable limit of lung function, it is critical to be able to predict the degree of functional impairment after multiple wedge resections. Many efforts have been made to predict postoperative lung function after anatomic resections for lung cancer6; to our knowledge, however, there exists no published description of the long-term impairment of lung function following pulmonary metastasectomy by wedge excisions. In their retrospective study of 66 pulmonary metastasectomy cases, Petrella et al7 found that patients who had undergone three or more nonanatomic resections had functional losses similar to those who had undergone a lobectomy procedure; however, they also reported that 3 months after the procedure, the patients who had undergone wedge resection had regained the postprocedural functional losses. Therefore, the long-term effects of this procedure on lung function remain unclear. We hypothesized that, analogous to the defined functional loss after anatomic resections, every additional wedge resection would cause a measurable functional impairment. Furthermore, we hypothesized that there would be a difference between the functional changes after anatomic resections, in which the central vessels and bronchi are occluded and anatomic units are removed, and the changes after nonanatomic resections, in which only alveoli containing parenchyma are removed from the lung. Knowledge about the exact extent of the functional loss after wedge resections should enable thoracic surgeons and pulmonologists to predict postoperative changes and that, again, will help preserve the desirable lower limit of lung function. Therefore, the current prospective observational study was performed to characterize and define the functional losses resulting from one or more wedge resections.