Pneumothorax is defined as air in the pleural space—that is, between the lung and the chest wall.1 Primary pneumothoraces arise in otherwise healthy people without any lung disease. Secondary pneumothoraces arise in subjects with underlying lung disease. The term pneumothorax was first coined by Itard, a student of Laennec, in 1803,2 and Laennec himself described the clinical picture of pneumothorax in 1819.2 He described most pneumothoraces as occurring in patients with pulmonary tuberculosis, although he recognised that pneumothoraces also occurred in otherwise healthy lungs, a condition he described as “pneumothorax simple”. The modern description of primary spontaneous pneumothorax occurring in otherwise healthy people was provided by Kjaergard in 1932.3 Primary pneumothorax remains a significant global problem, occurring in healthy subjects with a reported incidence of 18–28/100 000 per year for men and 1.2–6/ 100 000 per year for women.4 5 Secondary pneumothorax is associated with underlying lung disease, whereas primary pneumothorax is not. By definition, there is no apparent precipitating event in either. Hospital admission rates for combined primary and secondary pneumothorax are reported in the UK at between 5.8/100 000 per year for women and 16.7/100 000 per year for men. Mortality rates in the UK were 0.62/million per year for women and 1.26/million per year for men between 1991 and 1995.6 This guideline describes the management of spontaneous primary and secondary pneumothorax. It excludes the management of trauma. Algorithms for the management of spontaneous primary and secondary pneumothorax