Giant bullae may mimic tension pneumothorax radiologically so that it may expand completely to hemithorax, increase of radiolucency mediastinal shift, flattening of diaphragm and printing on trachea. Sixty one year old male patient with giant bullae misdiagnosed as tension pneumothorax and underwent to tube thoracostomy. The differential diagnosis of giant bullae and tension pneumothorax may be confusing. The therapeutic approaches of these two radiologically similar entities differ significantly. Thus proper physical assessment and radiological examination is crucial in the differential diagnosis and computed tomography examination should be performed before the adjustment of therapy.