Community-acquired pneumonia (CAP) is a common, serious disease of the lower respiratory tract, in which the lung tissues are colonized by one of a range of pathogens, from viruses to several types of bacteria, most notably the pneumococcus , Haemophilus influenzae, Chlamydia, Mycoplasma and Legio-nella. Hospital-acquired pneumonia occurs after admission to hospital for some other serious condition. Apart from the fact that patients in nursing homes are often frail and elderly, there is some evidence that when they develop pneumonia, the causative bacteria are generally similar to those that cause CAP. CRB65 is a well-established mnemonic that uses only the clinical evidence available to the doctor or nurse in the community, allowing immediate assessment and reassessment of the severity of CAP. Pneumonia is prone to cause complications in 5-20% of patients. Lung cancer can present as pneumonia, often with relatively few signs on examination.