A prospective cohort study of 129 consecutive patients developing pulmonary infiltrates in the surgical ICU was conducted to determine the predictors and outcome of pulmonary infiltrates. Most common etiologies of pulmonary infiltrates were pneumonia (30%), pulmonary edema (29%), acute lung injury (15%), and atelectasis (13%). Enteral nutrition was associated with a significantly lower incidence of acute lung injury as compared with pneumonia (22% vs 58%, p = 0.012). Patients with liver disease were significantly more likely to have pulmonary infiltrates due to acute lung injury as compared with other etiologies (p = 0.02). Clinical pulmonary infection score (Pugin score) > 6 virtually excluded acute lung injury, pulmonary edema, or atelectasis as etiologies of pulmonary infiltrates. Nosocomial Haemophilus/pneumococcal pneumonia occurred significantly earlier in the ICU as compared with Gram-negative (p = 0.05) or methicillin-resistant Staphylococcus aureus pneumonia (p = 0.01). Pneumonia in trauma patients was significantly more likely to be due to Haemophilus/pneumococcus as compared with all other ICU patients (54% vs 0%, p = 0.0004). These data have implications for treatment of patients with nosocomial pneumonia in the ICU.