Although the aetiology of postoperative nausea and vomiting is not completely clear, a number of key contributing factors increase the risk for an individual patient. The inhalational agents are variably associated with postoperative nausea and vomiting, and nitrous oxide is particularly emetogenic. Older inhalational anaesthetics, such as cyclopropane, are associated with a high incidence, while the currently used agents, isoflurane, enflurane and halothane, cause less, but still significant postoperative nausea and vomiting. Intravenous anaesthetics are also associated with differing degrees of emesis, though the newer agent, propofol, may be less emetogenic than the older anaesthetics. Opioids, used extensively throughout surgery, are further strong emetogens. Patient factors are also important--postoperative nausea and vomiting is three times more prevalent in adult females than in males, and children are around twice as susceptible as adults. Furthermore, a previous history of postoperative nausea and vomiting or motion sickness is a known risk factor. Superimposed on this is the type of surgery--abdominal and gynaecological surgery are particularly emetogenic, and the incidence of postoperative nausea and vomiting following strabismus surgery is high. Increased quality of healthcare, and a growing awareness of the importance of patient satisfaction, are providing new incentives to ensure that postoperative nausea and vomiting is dealt with adequately.