Ventilator-associated pneumonia is the most common health-care-associated infection in the intensive care unit (ICU) and computer-assisted diagnosis and surveillance is called for. The frequency of ventilator-associated pneumonia was assessed prospectively during a 6-month period in the ICUs of a teaching hospital in Tehran, Islamic Republic of Iran. To determine the accuracy of the Iranian Nosocomial Infections Surveillance (INIS) system, patient data were input to the software and compared with physicians’ judgement. The frequency of ventilator-associated pneumonia was 21.6%, or 9.96 episodes per 1000 ventilator days. The duration of admission to the ICU, duration of mechanical ventilator and number of re-intubations were significantly higher in patients who developed pneumonia. The INIS system identified 100% of cases, with no false-positive or false-negative results. Compared with developed countries, the frequency of ventilator-associated pneumonia was high in our ICUs, and INIS software was accurate in diagnosing nosocomial infection.