COPD is one of the top five killer conditions in the developed and the developing world. In the UK it is currently ranked number four but set to rise to number three in the rankings of years of life lost behind stroke and ischaemic heart disease.1 The natural history of COPD is characterised by progressive decline in airway function accompanied by the unpredictable occurrences of exacerbations. The importance of exacerbations in the natural history of the condition is now understood and embedded in recent clinical guidelines.2 Some exacerbations will result in a hospital admission and we know that the need for hospital admission signals a poor prognosis. Half of all patients admitted to hospital with an exacerbation of COPD will die within 4 years.3 Those patients who are admitted to hospital are also associated with increased risk with previous audit studies showing an in-hospital mortality rate of 7.4%.4 It is logical to think that improvements in hospital care of patients admitted with acute exacerbation would result in a reduction of mortality and that this would be some reflection on the quality of the service provided to the patient. In other circumstances, the use of the hospital mortality rate as a reflection of service quality would seem an excellent proxy. No one would doubt that improved survival after acute myocardial infarction or lower than average mortality rates for elective surgery would be a measure of the quality of service provided by the hospital. Walker et al have examined whether the mortality within 30 days of admission to hospital for an acute exacerbation of COPD can be used …