Nosocomial pneumonia is still a common problem, especially in intubated and mechanically ventilated patients. The endotracheal tube contributes substantially to the pathogenesis of pneumonia in these patients, because it facilitates microaspiration and impairs host defences. Common nosocomial pathogens like Pseudomonas aeruginosa are known to produce exopolysaccharide and generate the complex biofilm structure, which allows adhesion to abiotic surfaces and protection against antibiotic action. Multiple studies have identified bacterial biofilm on the inner lumen of endotracheal tubes, which represents a permanent source of infectious material. Endotracheal tubes, removed from patients with ventilator-associated pneumonia are covered more frequently with biofilm than those of uninfected controls. It remains unclear whether this represents a source of infection or contamination. Bacterial biofilm, however, may play an important role in recurrent pulmonary infections of the intubated and mechanically ventilated patient.