SummaryObjectiveThe aim of this study was to determine,a posteriori, the parameters detecting an event in a French medical emergency dispatching centre (SAMU).MethodsSix parameters were retained: total number of medical requests received by the Samu 93-centre 15: the number of decisions to send a mobile intensive care unit (MICU), number of decisions to send a non-medical unit, number of decisions to send a general practitioner and number of deaths observed by the physicians of the MICU. For each parameter, a daily referential was established over the five previous years (1998 to 2002) and compared with the results of August 2003.ResultsThe number of decisions to send a non-medical unit and the number of decisions to send a general practitioner were unchanged. The number of deaths on the 8th of August observed by the MICU physician should have led to an alert being given: 5.0 deaths for a referential of 1.7 (+ 194%). The number of decisions to send an MICU on the 7th of August should have led to an alert being given: 41 interventions for a referential of 25 (+64%). The number of medical interventions on the 6th of August should have led to an alert being given: 351 interventions for a referential of 299 (+17%).ConclusionThe total number of medical interventions treated by the SAMU 93-centre 15 is a the most sensitive and earliest marker of a sanitary event, such as that observed in August 2003 with the heat wave.