Evidence-based health care has become a priority in the National Health Service (NHS), with increased emphasis on clinical practices that are grounded in quality evidence rather than those that persist because of tradition. Turning and positioning of patients are well-accepted nursing activities. Appropriate positioning of the critically ill patient can dramatically improve gas exchange, resulting in a shorter stay in the critical care unit and an improved outcome. This study reviews the current published literature on the subject of positioning and gas exchange, with emphasis on oxygenation. Conclusions made from this study are that nurses need to be aware of how different positions can affect patients' oxygenation. Further research on exploring patients' experience of positioning within the critical care environment and nurses' understanding of positioning and oxygenation is needed.