The aim of this literature review is to sum up what is available knowledge about the effect of a medical emergency team (MET) system on three types of adverse events in general wards in hospitals; cardiac arrest, unexpected death and unplanned admission to an intensive care unit (ICU). Several studies have suggested that such adverse events are often preceded by warning signs, such as alterations of hearth rhythm, respiratory rate, blood pressure, oxygen saturation, mental status or urine output. Too often these warning signs are not recognized by the nursing staff, or appropriate action is not being undertaken. Therefore several hospitals, especially in the United Kingdom, USA and Australia, have developed so-called MET systems. The goal of these systems is early recognition of worsening of the patient’s clinical status and rapid intervention to stop the deterioration before the patient suffers a cardiac arrest, which has a poor survival rate. Fourteen papers were included in this literature review. There is no sufficient evidence that a MET system leads to a significant reduction in adverse events in hospitals. But all of the included papers, with the exception of one, showed an absolute reduction in adverse events. Our conclusion is that more high-quality research needs to be done in order to determine whether there is a significant effect of MET systems or not.