 The aims of the present multicentre study are 1 to quantify the prevalence of dyspnea in a large population of ICU mechanically ventilated patients, 2 to examine the link between the level of dyspnea and the occurrence of adverse events in the ICU, 3 to determine whether dyspnea in intensive care unit patients is associated with a higher length of stay in the ICU and a higher incidence of post traumatic stress disorder associated symptoms. 