The dispatcher plays a key role in allocating the right resource to patients in cases of medical emergency. In order to evaluate the performance of the dispatcher, it is necessary to analyse who is the caller, because this has an impact on the development of decision support systems. In the present study, all calls for an ambulance (n=565) during a one-week period at the dispatch centre in Uppsala, Sweden, were analysed with respect to the caller's relationship to the patient, the location of the caller, and the dispatcher's priority of the case. In emergencies, significantly fewer calls were made by the patients themselves, and significantly more callers had no relationship to the patient. In low priority cases most calls were made by healthcare providers. During a 2-week period we also analysed the physiological impairment of patients in cases dispatched as medical emergencies (n=595) by using the rapid acute physiological score. The rapid acute physiological score was significantly higher in the group dispatched as potentially life-threatening by the dispatcher compared with other emergencies. The study highlights the fact that dispatching often has to be carried out using second or third-hand information, and those patients prioritized as suffering from potentially life-threatening conditions have a more impaired physiological status.