[en] Pleural involvements are common and various respiratory diseases including inflammatory, infectious, occupational, or neoplastic pathological entities...Pleural thickening and pleurisy are usual radiological presentation. Etiological diagnosis imposes a vast and sometimes difficult exploration and it, especially since the conventional imaging by radiology, ultrasound, scanning and nuclear magnetic resonance has no specific diagnostic criteria for pleural malignancy. The metabolic imaging by positron emission tomography (PET) has been gradually positioned in the decision-making algorithm exploration of the pleural disease due to its excellent sensitivity in the diagnosis of malignant pleurisy (88.8%-100%). The analysis of chemistry, bacteriology and cytology pleural fluid makes a significant contribution to the diagnostic approach. However, although inescapable, thoracocentesis has a diagnostic sensibility not exceeding 62%. Moreover, the sensibility of the pleural blind needle biopsies does not exceed 51%. So, thoracoscopy, more invasive, is often justified to precise pleural disease with a diagnostic sensitivity greater than 95%. Finally, despite the diagnostic arsenal available, over 10% of pleurisies remain unknown etiology.