Congestive heart failure and cirrhosis are the most common causes of transudative pleural effusions, while pneumonia and malignancy are responsible for the majority of exudative effusions. Plain chest films are valuable in confirming the presence of an effusion, providing clues to the cause, and directing the method of pleural fluid sampling. Thoracentesis is safe and simple, and it is diagnostic in about 75% of cases. Pleural biopsy is indicated for unexplained exudative effusions, most of which are found to result from malignancy or tuberculosis. Medical thoracoscopy, if available, is the procedure of choice for patients with these effusions. Thoracoscopy permits visually directed pleural biopsies and allows for therapeutic intervention at the time of diagnosis, obviating the need for subsequent invasive procedures.