In intensive care patients, pneumonia acquired under ventilatory assistance is the second most frequent nosocomial infection after urinary tract infection. Duration of ventilatory assistance and stay in the intensive care unit are both increased in this leading cause of death due to nosocomial infection. A large number of studies and national and international consensus conferences have been devoted to determining precise criteria leading to clinical suspicion of pneumonia acquired under ventilatory assistance and the appropriate elements for bacteriological diagnosis. The criteria retained in these different studies are neither precise nor reproductable. Based on data in the literature and our their clinical experience the members of the Outcomerea association constituted working groups to elaborate a set of guidelines that could be applied in routine clinic in response to three questions: 1) what criteria are suggestive of pneumonia acquired under ventilatory assistance, 2) what bacteriological tools are needed to confirm diagnosis, 3) how and why should cure be defined. We present a review of the literature and the conclusions of the working groups.