Patients affected by pneumonia can be admitted in Intensive Care Units (ICUs) independently by the setting where the infection has been acquired (community, hospital, long-term care facilities); even more frequently pneumonia can develop in patients already hospitalized in ICU especially in those requiring mechanical ventilation for different reasons. Within the severe community acquired pneumonia requiring admission in ICU, the most frequently responsible micro-organisms are mainly represented by Streptococcus pneumoniae, but also by Legionella and Haemophilus. Pseudomonas aeruginona, anyway, cannot be excluded. The most recent Canadian and American guidelines for treatment of the above mentioned infections suggest the use of a combination therapy with beta-lactams (ceftriaxone, cefotaxime, ampicillin/sulbactam, piperacillin/tazobactam) and a new generation macrolide or respiratory fluoroquinolone. In case of allergy to beta-lactams, the association fluoroquinolone-clindamycin should be preferred. Whenever a Pseudomonas etiology is suspected because of the presence of risk factors such as COPD, cystic fibrosis, bronchiectasis, previous and/or frequent therapies with antibiotics and/or steroids, the same guidelines suggest the use of an anti-pseudomonas beta-lactam (such as piperacillin/tazobactam, carbapenems, cefepime) associated with an anti-pseudomonas fluoroquinolone (high doses ciprofloxacin). An anti-pseudomonas beta-lactam plus an aminoglycoside or aminoglicosyde plus fluoroquinolone can be an alternative. Early onset Hospital Acquired Pneumonia (HAP) and early onset Ventilator Associated Pneumonia (VAP) in patients without risk factors for multi-resistant etiological agents are generally sustained by S. pneumoniae, H. influenzae, methicillin-susceptible Staphylocccus aureus e Gram negative enteric rods. These infections can be treated with one of the following antibiotics: ceftriaxone or fluoroquinolones (moxifloxacin or ciprofloxacin or levofloxacin) or ampicillin/sulbactam or ertapenem. Late onset VAP and HAP in patients with risk factors for multi-resistant, by contrast, should be treated with a combination therapy: in case of defined or suspected P. aeruginosa, Klebsiella pneumoniae (ESbL+), Acinetobacter sp etiology, it is required the use of an anti-pseudomonas cephalosporin or an anti-pseudomonas carbapenem or b-lactam + beta-lactamase inhibitor associated with an anti-pseudomonas fluoroquinolone or an aminoglicoside. The possible presence of MRSA or Legionella pneumophila suggests the use of anti-Gram positive antibiotics such as glycopeptides or linezolid. These quidelines confirm the role of ciprofloxacin combined with beta-lactams whenever P. aeruginosa, Klebsiella pneumoniae (ESbL+), Acinetobacter sp. etiology is suspected.