Questions › Category: Medicine › What's a large pneumothorax? 0 Vote Up Vote Down student asked 7 years ago What’s the definition of a large pneumothorax? What's a large pneumothorax? 1 Answers 1 Vote Up Vote Down Best Answer admin Staff answered 7 years ago According to The British Thoracic Society guidelines a large pneumothorax measures >2 cm at the level of the hilum. Answer for What's a large pneumothorax?