Severe community acquired pneumonia (CAP) is defined as CAP that has to be treated in an Intensive Care Unit (ICU). Treatment in the ICU may be needed because of: a) acute respiratory failure, b) hemodynamic instability, c) monitoring and treatment of dysfunction of other organs or systems. Thus severe CAP is CAP that results in severe sepsis or multiple organ failure. Severe CAP is a syndrome with high mortality (20-50%), that demands early recognition and immediate and aggressive treatment. At the same time an effort should be made to isolate responsible pathogens, utilizing in selected cases, invasive diagnostic techniques. Objective criteria can help to recognize these high risk patients. Empirical treatment should provide adequate coverage for S. pneumoniae, Gram (-) bacilli and Legionella pneumophila. Pneumon 2003, 16(2):126-141.