Severe or life-threatening pneumonia make up an important public health problem and take place in various clinical practice guidelines. Besides all hospital-acquired pneumonia cases, community-acquired pneumonia cases who need hospitalization (Group 3) and intensive care (Group 4), also must be considered in life-threatening pneumonia group with their relative high mortality rates. Moreover pneumonia that develop in immune-suppressed cases are also severe and life-threatening. While mortality rate is generally 1-5% in community-acquired pneumonia cases that are followed as outpatients, it is 5-25% in those who are hospitalized and around 30-50% in hospital-acquired pneumonia cases. Pneumonia in cases with underlying diseases like COPD, heart or kidney failure, diabetes mellitus, in old, alcoholics and immune-supressed patients has a tendency to proceed more severe. Although microorganisms causing community-acquired pneumonia are different in various studies, Streptococcus pneumoniae is the commonest typical type of pathogen with 30-50% percentile. Haemophilus influenzae and Staphylococcus aureus are relatively common in the ones with chronic diseases and in old cases due to frequency gram-negative bacillus colonisation. Moraxella catarrhalis is also reported to be an agent. Besides all these, Legionella pneumophyla, Mycoplasma pneumoniae, Chlamydia pneumoniae, gram negative bacilli, Chlamydia psittaci, Coxiella burnetti, Burkholderia pseudomallei, Bacillus cereus, Pneumocystis carinii, Varicella and adenoviruses are also known as causative agents. Mortality related directly to the disease is increased in hospital-acquired pneumonia with bacteriemia, old patients (>60 years), and pneumonia associated with ventilators. Early and correct diagnosis, starting the therapy with convenient antibiotics without being late, continuing the therapy in appropriate doses and periods, close monitorization of all the vital functions of the cases and applying all types of palliative therapy procedures when needed are factors that could be effective in decreasing the mortality.