The presence of emphysema may lead to an underestimation of postoperative respiratory function after lobectomy when evaluated by standard functional assessment. The aim of the study was to assess the correlation between computed tomography (CT) densitometry, pathological grading of emphysema and variation of pulmonary function after lobectomy for lung cancer. Forty-one patients entered the study. Respiratory function was assessed preoperatively and after a mean period of 4.04 months following surgery. Postoperative function remained unchanged or increased after surgery in nine patients (Group A). In the remaining 32 patients (Group B) postoperative function was reduced after surgery. Preoperative forced expiratory volume in 1 s (FEV(1))% was 68.5+/-13.1% in Group A and 91.7+/-21.0% in Group B. CT densitometry of the lobe to be resected was -877.8+/-57.6 HU in Group A and -827.5+/-64.4 HU in Group B. Pathological grading of emphysema of the resected lobe (range 0-10) was 4.1+/-2.2 in Group A and 3.1+/-1.2 in Group B. A significant correlation was observed (Spearman rank correlation) between the variation of FEV(1) and preoperative FEV(1) (P=0.003; r=-0.455), CT quantitative assessment (P=0.036; r=-0.430) and pathological grading (P=0.008; r=0.673). Patients with a higher degree of emphysema had a lower reduction of respiratory function after lobectomy and CT densitometry and pathological grading of emphysema correlated with the variation in respiratory function.