To predict the postoperative improvement in performance status after bullectomy, preoperative pulmonary function and dyspneic grade were evaluated in 20 patients with giant bulla. The patients were divided into two groups, based on postoperative performance status: group 1 consisted of 15 patients with improved status after surgery; and group 2 of five patients with worsened status after temporary improvement. To determine correlation with the groups, preoperative functional measurements such as %VC, FEV1%, MMF, PEFR, RV/TLC, delta N2, LCI, and PNCD were then analyzed by the multivariate statistic method; results of delta N2 and FEV1% showed significant correlation with the groups. Prediction of the groups based on the two measurements agreed with the actual results except in one patient. These results show that postoperative improvement in performance status of patients with giant bulla can be predicted on the basis of preoperative pulmonary function.