The incidence of a tension pneumothorax is very low. The initial treatment of a tension pneumothorax is needle thoracocentesis. This procedure is not a routine treatment and this invasive treatment is not without risks. Recognition of a clinically relevant tension pneumothorax remains difficult especially in the prehospital setting. Elevation of one half of the chest is a notoriously unreliable observation in relation to the diagnosis of tension pneumothorax. Absence of breath sounds without tension physiology is not a reason to perform a thoracocentesis. With the help of 3 cases we would like to explain and clarify the clinical presentation, the indication for and the correct procedure of thoracentesis.