OBJECTIVE: To determine whether statins protect against all cause mortality after a diagnosis of pneumonia. DESIGN: Cohort study using propensity score based method to control for differences between people prescribed and not prescribed statins. SETTING: United Kingdom Health Improvement Network database, which contains electronic primary care medical records of more than six million patients. PARTICIPANTS: Every patient starting a statin between 1995 and 2006 (129,288) matched with up to five non-statin users (n = 600,241); 9073 patients had a recorded diagnosis of pneumonia, of whom 1398 were using a statin. MAIN OUTCOME MEASURE: All cause mortality within six months of diagnosis of pneumonia. RESULTS: Among users and non-users of statins with comparable propensity scores, 95/942 users and 686/3615 non-users died on the day that pneumonia was diagnosed. In the following six month period, 109/847 statin users died compared with 578/2927 non-users, giving an adjusted hazard ratio of 0.67 (0.49 to 0.91). If these observed benefits translated into clinical practice, 15 patients would need to be treated with a statin for six months after pneumonia to prevent one death. CONCLUSIONS: Compared with people who were not taking statins, the risk of dying in the six month period after pneumonia was substantially lower among people who were already established on long term statin treatment when the pneumonia occurred. Whether some or all of this protective effect would be obtained if statin treatment begins when a patient first develops pneumonia is not known. However, given that statins are cheap, safe, and well tolerated, a clinical trial in which people with pneumonia are randomised to a short period of statin treatment is warranted.