Nosocomial pneumonia is a common complication of mechanical ventilation. However the actual incidence of pneumonia associated with ventilator is not known. A total of 57 consecutive patients submitted to mechanical ventilation(MV) for mqre than 48 hours in ICU were studied to investigate the incidence, etiology and consequence of ventilator associated pneumonia. Pneumonia was diagnosed when new and persistent radiographic infiltration was detected together with more than two of the following criteria; (l) fever more than 38degrees C, (2) leukocytosis more than 12000/mm, (3) purulent sputum with s gram stain showing bacteria. The results are as following: l) Twenty-one(37.9%) patients developed bacterial pneumonia during mechanical ventilation 2) Ventilator associated pneumonia was developed after 4.6 days of machanical ventilation 3) The etiology of pneumonia were Gram(-) bacilli 65.8%, Gram(+) bacilli 31.7% and, Pseudomonas 27.9%, Streptococcus 16.5% and or, Staphylococcus 13.9%.