Background: Ventilator-associated tracheobronchitis (VAT) is considered an intermediate condition between bacterial airway colonization and ventilator-associated pneumonia (VAP). The purpose of this prospective cohort study was to further characterize VAT in terms of incidence, etiology, and impact on patient outcomes. Methods: Patients intubated for > 48 h in the surgical and medical ICUs of Barnes-Jewish Hospital were screened daily for the development of VAT and VAP over 1 year. Patients were followed until hospital discharge or death, and patient demographics, causative pathogens, and clinical outcomes were recorded. Results:A total of 28 patients with VAT and 83 with VAP were identified corresponding to frequencies of 1.4% and 4.0%, respectively. VAP was more common in surgical than medical ICU patients (5.3% vs 2.3%;P<.001), but the occurrence of VAT was similar between surgical and medical patients (1.3% vs 1.5%;P = .845). VAT progressed to VAP in nine patients (32.1%) despite antibiotic therapy. There was no significant difference in hospital mortality between patients with VAP and VAT (19.3% vs 21.4%;P = .789). VAT was caused by a multidrug-resistant (MDR) pathogen in nine cases (32.1%). Conclusion: VAT occurs less commonly than VAP but at a similar incidence in medical and surgical ICU patients. VAT frequently progressed to VAP, and patients diagnosed with VAT had similar outcomes to those diagnosed with VAP, suggesting that antimicrobial therapy is appropriate for VAT. VAT is also frequently caused by MDR organisms, and this should be taken into account when choosing antimicrobial therapy.