A prospective observational study was conducted in a neonatal intensive care unit to identify factors associated with the development of ventilator-associated pneumonia (VAP) in 170 infants aged less than 30 days who required mechanical ventilation for longer than 48 hours. VAP occurred in 85 infants (50 cases per 100 mechanically-ventilated infants) or 70.3 cases per 1,000 ventilator days. Stepwise logistic regression analysis identified 3 factors independently associated with VAP: umbilical catheterization [adjusted odds ratio (AOR)=2.5; 95% confidence interval (CI)=1.3 to 4.7; p=0.007]; respiratory distress syndrome (AOR=2.0; 95% CI=1.0 to 3.9; p=0.03); and insertion of orogastric tube (AOR=3.0; 95% CI=1.3 to 7.2; p=0.01). Infants with VAP had longer duration on ventilator (14.2 days vs 5.9 days; p<0.001) and longer hospital stay (28.2 days vs 13.8 days; p<0.001). Organisms were isolated in 42 specimens (49.4%) from endotracheal aspirate culture and in 17 specimens (20.0%) from hemoculture; Pseudomonas aeruginosa, Klebsiella pneumoniae and Acinetobacter spp were predominant. Polymicrobial infection was found in 11 specimens (12.9%) from endotracheal aspirate culture. Leukocytosis and blood gas values could not predict the presence of VAP. The mortality of infants with VAP (29.4%) did not differ significantly from that of infants without VAP (30.6%) (p=0.87). Certain clinical interventions might potentially affect the incidence of VAP and outcome associated with VAP.