The aim of this study was to determine the incidence, the organisms responsible for and the impact on outcome of nosocomial tracheobronchitis (NTB) in the intensive care unit (ICU). This prospective observational cohort study was conducted in a 30-bed medical/surgical ICU over a period of 6.5 yrs. All patients ventilated for >48 h were eligible. Patients with nosocomial pneumonia (NP) without prior NTB were excluded. Patients with first episodes of NTB were compared with those without NTB by univariate analysis. The study diagnosed 201 (10.6%) cases of NTB. Pseudomonas aeruginosa was the most common bacteria. NP rates were similar in patients with NTB compared with patients without NTB. Even in the absence of subsequent NP, NTB was associated with a significantly higher length of ICU stay and duration of mechanical ventilation in both surgical and medical populations. Mortality rates were similar in NTB patients without subsequent NP compared with patients without NTB. Antimicrobial treatment in NTB patients was associated with a trend to a better outcome. Nosocomial tracheobronchitis is common in mechanically ventilated intensive care unit patients. In this population, nosocomial tracheobronchitis was associated with longer durations of intensive care unit stay and mechanical ventilation. Further studies are needed to determine the impact of antibiotics on outcomes of patients with nosocomial tracheobronchitis.