Out of more than 3 000 diagnostic thoracoscopies carried out in the Chest Hospital Heckeshorn since 1950, a pneumothorax was induced in 43% because of pulmonary lesions and in 16% because of disease of the mediastinum or of the thoracic wall. The pathologic changes can be differentiated more exactly by the use of telescopes than by the naked eye. Biopsies can be taken from several different points under visual control. We did not observe major bleedings in our cases with biopsy specimens as large as raisins. The post thoracoscopic suction drainage should be performed through tubes with a caliber of 8 mm and with multiple side holes. A negative pressure of 100 mbar and a pumping flow of more than 3, 51/min has to be applied. The mean time for drainage was 3.4 days, long-lasting fistulas were not seen. A protective antibiotic therapy can be discussed after five days of intrapleural suction. 87% of the lung biopsies revealed a specific morphological diagnosis. In only 13% of the cases additional open biopsy was indicated. This gave new informations in about one half, in the remaining cases the thoracoscopic findings were confirmed. We used the rigid 8 mm-thoracoscope (Storz) with a cold-light source. Only one trocar and one cannula are necessary because observation, photography biopsy, puncture, suction and diathermy are possible through the one-channel thoracoscope. In our opinion, flexible fiberoptics have more disadvantages than advantages.