This article examines the main features of acute respiratory distress syndrome (ARDS), including the pathophysiology, clinical manifestations, complications and treatment. Patients with ARDS are critically ill and require close monitoring and mechanical ventilation in an intensive care unit. The benefits of prone positioning, one of the main treatment options for these patients, are discussed in detail. By understanding the physiological principles that underpin the prone position, the critical care nurse will be more effective in identifying patients who might benefit from this treatment.