A diagnosis of tension pneumothorax is usually only considered within the context of trauma, incorrect chest drain insertion or positive pressure ventilation. Four patients are presented who developed spontaneous tension pneumothorax with no precipitating factors. In three of these instances, the diagnosis was only made radiologically and in every case the treating physician was unaware that a spontaneous tension pneumothorax could occur. Previously, emphasis has been placed on tracheal deviation in a tension pneumothorax. However, this is an inconsistent finding as one of the cases highlights. Patients may appear surprisingly clinically well until they decompensate. These cases are highlighted to raise awareness of this potentially life threatening condition.