Chronic empyema thoracis results from various etiologies. Improvement in pulmonary function after empyemectomy and decortication has proved difficult to predict when the etiology of chronic empyema thoracis is tuberculosis. The purpose of this study was to confirm the changes in pulmonary function according to the etiology after an operation. Sixty-five patients were classified into two groups according to their etiology: Group A (tuberculous) and Group B (non-tuberculous), and they were retrospectively evaluated with regard to their forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), percentage of predicted normal value of FEV1 (% FEV1) and FVC (%FVC). Empyemectomy and decortication was performed for all the patients and the two groups were similar in age, gender and preoperative spirometric parameters. In Group A (n=41), the pre- and postoperative mean values were 2.31L and 2.88L in FEV1, 65.8% and 80.5% in %FEV1, 2.62L and 2.55 L in VC, 61.9% and 71.8% in %VC, respectively. In Group B (n=24), the pre- and postoperative mean values were 2.13L and 2.49L in FEV1, 66.4% and 73.8% in %FEV1, 2.55L and 2.95 L in FVC, 64.9% and 71.8% in %FVC, respectively. All the spirometric parameters improved significantly in both groups compared to their preoperative values. However, no significance was shown in the rate of increase of the spirometric parameters between the two groups. In conclusion, improvement of lung function is expected after empyemectomy and decortication, regardless of the etiology of the chronic empyema thoracis.