100 thoracic surgery patients were intubated by means of a left-hand Broncho-Cath PVC Double-Lumen Tube (DLT) and 10 further patients with a right-hand tube. In 76 of the 100 left-hand DLT's safe conventional placement of the tube was successful, oriented exclusively by auscultation findings and positive pressure respiration. However, fibre-optic control showed that only 44 of these tubes were correctly positioned (57.1%). 25 DLT's were too high and 24 too low, whereas the right main bronchus had been intubated in 6 cases. 1 DLT was endoscopically correctly placed although the positioning of the tube had been considered unsatisfactory during conventional examination. Only 2 right-hand DLT's fulfilled the conventional and endoscopic criteria for correct placement of the tube. All malpositionings could be corrected via fibre optics. Recurrent tube dislocations occurred both after lateral repositioning of the patients (so that they were now lying sideways) (27.3% of all patients) and intraoperatively (24.6% of all patients). Besides, intraoperative obstructions of the tube/bronchus lumen due to blood/coagulates (49.1% of the patients) and/or secretion (46.4% of the patients) could be demonstrated and eliminated by endoscopy. Fibre bronchoscopy proved to be a decisive help to reduce the possibilities of complications associated with the use of the Broncho-Cath PVC-DLT in thoracic surgery.