Pneumothorax (PTX) is the most common complication associated with percutaneous needle aspiration (PNA) of the lung. Age, sex, cooperation, and lesion size, location, and depth, as well as needle size, number of passes, and radiographic calculation of total lung capacity all have been implicated in influencing the rate of PTX. Pulmonary function testing to assess PTX risk in PNA has not been previously examined. We retrospectively reviewed 159 patients undergoing PNA who had preprocedure spirometry (PFT) and chest roentgenogram (CXR) interpreted for changes of obstruction or restriction to determine if these classifications could stratify patients at high risk for PTX. We also examined single variables to determine their predictive power. Patients with normal PFT and CXR had a 10 percent risk of PTX, and only one such patient needed intervention to treat the PTX. Obstruction by PFT, regardless of CXR findings, predicted a 50 percent PTX rate. Among single variables, FEV1 proved to be the most significant predictor of PTX. Preprocedure spirometric testing can enhance the assessment of PTX risk and should be routinely performed prior to needle aspiration.