Purpose: To determine whether the practice of not routinely changing ventilator circuits in patients who require prolonged mechanical ventilation is associated with ventilator-associated pneumonia (VAP)., Methods: Patients were divided into two groups, ventilator circuits were routinely changed every 7 days for the control group (39) and every 14 days for the experimental group (40) over a period of 1 yr (April 1, 2009-March 31, 2010). Pediatric patients (age 17 yr or less) were not included. VAP was diagnosed by the criteria of the Centers of Disease Control and Prevention (CDC). Incidence of VAP and characteristics of infection were evaluated., Results: In the experimental group, 2 episodes of pneumonia were observed in 40 patients and 1,322 ventilator days. The rate of VAP was 1.5 per 1,000 ventilator days. There was 1 episode of pneumonia in 39 patients and 481 ventilator days for the control group. The rate of VAP was 2.1 per 1,000 ventilator days. The difference between both groups was not significant (p=.695)., Conclusion: Extending ventilator circuit change interval from 7 days to 14 days does not increase the risk for VAP.