Thoracoscopy, which was formerly used in active tuberculosis to divide pleuro-pulmonary adhesions and to complete therapeutic pneumothorax, has now become the object of renewed interest. By introducing, after pneumosera and usually into the 4th to 8th intercostal space in the axillary line, a fine trocar into the chest, the whole thoracic cavity, including parietal pleura, diaphragm, lung and fissures, mediastinum and pericardium, can be explored. This technique, performed under local rather than general anaesthesia or under neuroleptanalgesia, is innocuous, inexpensive and effective. In addition, the patient is immobilized for only 4 or 5 days on average and the technique is much less taxing than surgery, which can be avoided in many cases. Thoracoscopy nowadays is mainly used to determine the cause of chronic pleurisy unexplained after 3-4 weeks (positive pleural biopsies are obtained in 92-97% of cancerous or tuberculous patients). Thoracoscopy is half-way between purely medical practice and surgery and deserves to be widely used again by pneumologists, provided they learn to master the technique by regular, assiduous and adequate use.