This prospective cohort study of 581 critically ill trauma patients evaluated 25 risk factors for nosocomial pneumonia. All critically ill multiple trauma patients meeting the inclusion criteria were enrolled in the study within 48 hours of admission. Subjects were primarily male (72%) and received a blunt injury (84%); 156 patients (26.8%) developed clinically defined nosocomial pneumonia, which on average was diagnosed on day 6.4 ± 4.1. Early-onset pneumonia developed in 85 patients and 71 patients had late-onset pneumonia. Predictor variables were selected by univariate analysis and if significant, subjected to multivariate analysis by forward stepwise logistic regression. To identify predictors of early onset nosocomial pneumonia, regression analysis was rerun excluding patients with late onset nosocomial pneumonia, and the opposite to identify predictors of late-onset nosocomial pneumonia. Treatment, head injury, and chest injury explained 60.2% of the variance, and with 14 significant individual indicators, correctly classified 81.4% of patients (90.1% of patients without and 58.2% of those with pneumonia). The model for early onset nosocomial pneumonia classified 85.3% of patients (95.8% of those without pneumonia and 32.9% of those with early-onset pneumonia). The model for late-onset nosocomial pneumonia classified 87.1% of patients (95.5% of those without pneumonia and 36.6% of those with late onset pneumonia). The results of this study suggest that treatment, head injury, and chest injury underlie the individual indicators for nosocomial pneumonia. Treatment, head injury, chest injury, age, and receiving antibiotics were significant predictors of early onset pneumonia and patients who received antibiotics were less likely to develop it. Treatment, head injury, chest injury, age, and days of mechanical ventilation were significant predictors of late onset pneumonia. The identified predictive models will allow early identification of patients at high risk of developing pneumonia so preventive measures can be implemented.