Despite of extensive use of antibiotics for respiratory tract infections pleural empyema is still seen as a complication to pneumonia (7-10 cases/100.000 inhabitants pr. year). Pleural empyema as a complication to pulmonary surgery is reported in 2-3% of the patients even with use of antibiotic prophylaxis. Pleural empyema is most often a serious disease of long duration. The diagnosis is obtained with microbiological and histological examination of the pleural fluid. Mixed infection occurs in over half of the cases, most often including anaerobic bacteria, but most human pathogens have been reported as etiological agents. Treatment includes drainage of pus and administration of relevant antibiotics, systemically and pleurally. Drainage can be performed via thoracocentesis, by tubes, or by resection of a part of the rib. The optimal treatment strategy is so far unknown, since good prospective comparative clinical studies are lacking.