PURPOSE: We evaluated the usefulness of quantitative spiral CT to predict postoperative lung function in patients undergoing pulmonary resection. MATERIALS AND METHODS: Fourteen patients in whom pneumonectomy or segmentectomy were performed underwent preoperative chest spiral CT and pulmonary function test(PFT). Six patients underwent postoperative follow-up PFT. Ten patients underwent preoperative radioisotope(RI) lung perfusion scan. Preoperative CT data were postprocessed with contiguous pixel method ranged from -9107HU to -500HU to quantify total functional lung volume(TFLV) and regional volume to be resected(RFLV). Postoperative lung function was predicted by following formula;Predicted postoperative PFT value=preoperative PFT x 1-RFLV/TFLV). CT predicted value was compared with postoperative measured PFT value and those value of RI perfusion scan. RESULTS: CT predicted values were very close to postoperative measured value and RI predicted value, and were correlated well with postoperative measured values (FVC: r=0.988, P<0.001 ;FEV1: r=0.994, P<0.001) and RI predicted values (FVC :r=0.976, P<0.001 ;FEVl: r=0.974, p<0.001). CONCLUSION: Quantitative spiral CT was useful to predict postoperative lung function and could be an effective alternative to RI perfusion scan.