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© 2006 Elsevier Ltd. All rights reserved. Development of a sterile, exudative pleural effusion (simple parapneumonic effusion) is a common complication of bacterial pneumonia, and the majority of cases resolve with antibiotic treatment alone. A minority become secondarily infected (complex parapneumonic effusions), and require chest drainage for clinical resolution. Infected pleural fluid is characterized biochemically by a low pH and glucose, and an elevated lactate dehydrogenase. Pleural infection is associated with activation of the coagulation cascade, and the subsequent deposition of fibrin within the pleural space results in the formation of septations and impedes drainage. Ongoing infection leads to the accumulation of pus in the pleural cavity (empyema). Treatment of pleural infection comprises appropriate antibiotics, chest drainage, nutritional support, and in some cases surgery; intrapleural fibrinolytics are ineffective. Tuberculous pleural effusions develop as a result of a delayed hypersensitivity reaction to mycobacteria in the pleural space. Diagnosis is based on mycobacterial culture of pleural fluid or pleural tissue, or may be inferred from the finding of granulomas on pleural biopsy. Treatment of tuberculous pleurisy involves the same antimicrobial regimen as that used for pulmonary tuberculosis. The use of steroids to treat tuberculous pleurisy is controversial, although they may lead to symptomatic benefit by hastening pleural fluid absorption.