Appropriate antibiotic treatment reduces the duration of symptoms associated to pneumonia, the risk of complications and mortality. In most cases, it is not possible to identify the etiologic agent so antibiotic treatment is empirically prescribed. In Chile, one third of Streptococcus pneumoniae strain isolates has diminished susceptibility to penicillin; in-vitro erythromycin resistance is about 10-15% and cefotaxime resistance 2-10%. It is recommended to classify patients with community acquired pneumonia in four risk categories: Group 1: patients under 65 years without co-morbidities, in ambulatory attendance. Treatment: oral amoxicillin 1 g TID, 7 days. Group 2: patients over 65 years and / or co-morbidities, in ambulatory attendance. Treatment: oral amoxicillin/clavulanate 500/125 mg TID or 875/125 mg BID, or cefuroxime 500 mg BID, 7 days. Group 3: patients admitted to general wards with criteria of moderate severity. Treatment: ceftriaxone 1-2 g once a day or cefotaxime 1 g TID, IV, 7-10 days. Group 4: patients with severe CAP that must be interned into ICU. Treatment: ceftriaxone 2 g once a day or cefotaxime 1 g TID, IV, associated to erythromycin 500 QID, levofloxacin 500-1.000 mg once a day, or moxifloxacin 400 mg/once a day, IV, 10-14 days. In the presence of allergy to or treatment failure with betalactam drugs and/or positive serology for Mycoplasma, Chlamydia or Legionella sp it is recommended to add: erythromycin 500 mg QID, IV or oral, oral clarithromycin 500 mg BID, or oral azythromycin 500 mg once a day