The frequency and the various etiologies of community acquired pneumonia are not well established. In adults, it is believed that half of the cases are caused by viruses and Mycoplasma pneumoniae. The pneumonia in these patients is limited and treated on an ambulatory basis. In patients who need to be hospitalized, the main etiology of pneumonia is S. pneumoniae. Despite effective antibiotic treatment, pneumococcal pneumonia still remains a life-threatening infection, especially in bacteremic patients presenting with underlying predisposing factors such as renal insufficiency, liver cirrhosis, and age over 70. In order to prevent the morbidity and mortality due to pneumococcal pneumonia, vaccination of the high-risk population on a larger scale than at present should be considered.