Considerable clinical experience confirms that oxygenation can be improved in many patients with ARDS by employing prone ventilation. The improvement occurs because, in the prone position, the lung fits into the thorax such that lung distention is more uniform and compressive forces extant in the supine position, which serve to cause dorsal airspace collapse, are reduced. Whether these changes translate into improved clinical outcomes has yet to be determined, but prone ventilation has the potential of reducing oxygen toxicity and limiting ventilator-induced lung injury.