Background: Ventilator associated pneumonia (VAP) is a type of nosocomial pneumonia associated with increased morbidity and mortality. Awareness about the risk factors can be used to implement simple and effective preventive measures. Objectives: To determine the factors associated with development of VAP and its microbial profile among patients admitted to ICUs. Methods: A nested case-cohort study was conducted at Al-Hussein university hospital in Cairo city, Egypt for a period of 6 months from the 1 st of March 2013 to the end of August 2013. Patients who were on mechanical ventilation (MV) for more than 48 hours were monitored at frequent intervals for development of VAP. Samples obtained by endotracheal aspiration were ccultured on Blood agar-Chocolate agar-MacConkey agar, plates of which were incubated at 37c for 24 hours. The isolated organism was identified by morphological and biochemical identification. Results: Of the 73 samples which were taken from endotracheal tubes of the patients, 42 cases were diagnosed as VAP with an incidence rate of 57.5%. Early onset VAP occurred in 36 (85.7%), while late onset VAP was observed in the remaining 6 patients(14.3%). Escherichia coli (40.5%) followed by Klebsiella pneumoniae (23.8%) were the most commonly isolated pathogens. Univariate analysis showed that the duration of MV and ICU stay, re-intubation, supine head position, impaired consciousness, steroids use and H2 blocker use were the risk factors associated with VAP (p < 0.05). Logistic regression revealed duration of MV as an independent risk factor for VAP. Conclusion: The incidence of ventilator pneumonia is high in our study. VAP was significantly related to duration of MV and ICU stay, re-intubation, supine head position, impaired consciousness, steroids use and H2 blocker use.