Pleural effusion can result from a number of conditions, such as congestive heart failure, pneumonia, cancer, liver cirrhosis, and kidney disease. The characteristics of the fluid depend on the underlying pathophysiologic mechanism. The fluid can be transudate, nonpurulent exudate, pus, blood, or chyle. Imaging studies are valuable in detecting and managing pleural effusions but not in accurately characterizing the biochemical nature of the fluid. Ultrasound is more sensitive than physical exam and chest radiography to detect and characterize pleural fluid, and avoids many negative aspects of computerized tomography (CT). Ultrasound can be used to assess pleural fluid volume and character, revealing possible underlying pathologies and guiding management.. Objective. To review the use of ultrasound for the detection of pleural effusions and guidance of the thoracentesis procedure. Pleural aspiration describes a procedure whereby pleural fluid or air may be aspirated via a system inserted temporarily into the pleural space. This may be for diagnostic purposes (usually removing 20–50 ml fluid) or therapeutic to relieve symptoms. In the literature it is varyingly called thoracocentesis, thoracentesis or pleural aspiration.