Pleural diseases frequently pose problems to the pulmonary physician. The clinical and radiological approaches are often insufficient and it is necessary to resort to techniques which enable a precise morphological diagnosis of the pleural lesion. Starting with a needle puncture and biopsy, the medical investigation of the pleura has been enriched by thoracoscopy which enables visualisation of not only the parietal and visceral pleura and the lung but also the mediastinum and the pericardium. Using this technique the diagnostic yield and the harmless nature of the technique are of the first importance. After recording traditional techniques of investigation of lung disease (puncture, needle biopsy) the equipment, the technique, the indications and the risks and the diagnostic results from thoracoscopy are discussed.