This paper describes a cohort study of patients admitted to any of three ICUs in an academic tertiary care center who required mechanical ventilation for longer than 24 hours.  Stepwise logistic regression analysis identified four factors that were independently associated with risk of VAP: organ system failure, patient age > 60 years, impaired functional status prior to hospitalization, and supine head positioning (<30 degrees of elevation) during the first 24 hours of mechanical ventilation.