The combination of two rare complications in intensive care caused an acute life-threatening situation. Following puncture of the left subclavian vein a pneumothorax developed over the course of a couple of days. The inserted thoracic drain dislocated into the subcutaneous tissue. During the induction of anaesthesia and controlled ventilation a tension pneumothorax developed. A decrease in oxygen saturation and an increase in the ventilation pressure led first to the diagnosis "malposition of the double lumen endotracheal tube", but its correct position could be confirmed by bronchoscopy. Finally, the tension pneumothorax was diagnosed by x-ray of the chest. This life-threatening situation could be treated by the insertion of a thoracic drain. The operation could be performed without any problems.