The optimal fluid for the resuscitation of critically ill and injured patients remains the subject of considerable controversy. Hypertonic crystalloid solutions such as hypertonic saline provide rapid volume expansion, have an acceptable safety profile, and are easy to store and transport. Recent meta-analyses suggest a trend toward increased survival in patients given hypertonic saline, and it has been suggested that they may have particular benefit in certain groups of patients such as hypovolaemic head injury patients. This short review examines the physiological and experimental evidence supporting the use of hypertonic saline in fluid resuscitation.