High-flow nasal cannula oxygen (HFNC) is a relatively new therapeutic innovation being used in adults with severe respiratory disease. It delivers heated humidified oxygen through short nasal prongs and supplies much higher flow rates than traditional nasal cannula systems. These higher flows match patient flow demands better, reduce anatomic dead space and provide a slightly positive pressure in the upper airway. Randomized trials, nonrandomized prospective trials and case series using HFNC in adults were identified in the PubMed, Google Scholar and Cochrane databases for the period of June 1981 to December 2013. Fifteen studies meeting our inclusion criteria were analyzed; 5 were randomized controlled studies. These studies included 943 patients managed in intensive care units. Common clinical diagnoses included postoperative status, cancer and pneumonia. These studies demonstrated that HFNC provided better or comparable oxygenation when compared with conventional face masks and nasal cannulas. Side effects included epistaxis, nasal discomfort and dryness. No unexpected side effects were reported in the studies reviewed. Current studies demonstrate that HFNC can improve oxygenation adults with hypoxemic respiratory failure. In some patients, it is superior to traditional oxygen delivery systems and may obviate the need for positive pressure ventilation. More studies are needed to compare HFNC with noninvasive ventilation.