One of the most challenging problems in critical care medicine is the acute respiratory distress syndrome (ARDS), the most severe form of acute lung injury (ALI). Evidence from experimental studies suggests that mechanical ventilation can cause or aggravate lung injury. Referred to as ventilator-induced lung injury (VILI), this condition resembles ALI and ARDS, and is difficult to identify in humans because its appearance overlaps the underlying disease, supporting the assumption that mechanical ventilation can extend the severity of pre-existent lung injury. There is increasing laboratory evidence that ventilating ARDS models with relatively low tidal volumes and high levels of positive end-expiratory pressure (PEEP) is clinically beneficial. In 2000, the ARDS Network published reported a reduced mortality (from 40% to 31%) in a mixed population of patients with ALI and ARDS ventilated with half the tidal volume of the control group. However, almost forty years after the first description of ARDS, many investigators and experts in the field still apply essentially the same ventilatory strategy (tidal volume greater than 10 mL/kg body weight and PEEP levels less than 10 cmH2O) as in the original description of ARDS.