The first wave of the 2009 influenza A(H1N1) epidemic occurred on the islands of Réunion and Mayotte during the southern hemisphere winter. The limited knowledge available regarding the virus’s virulence, combined with the onset of seasonal influenza, necessitated the implementation of non-specific, reactive surveillance systems. Activity data from sentinel network physicians revealed an epidemic peak in week 35 in Réunion and week 37 in Mayotte. Daily analysis of emergency department visit data via the Oscour® system showed an identical temporal trend for both systems in Réunion (epidemic peak in week 35). In Mayotte, the peak in emergency department activity was observed in week 39, two weeks after the peak observed by the sentinel physician network. The various data sources used demonstrated high consistency and complementarity, enabling appropriate monitoring of this first epidemic wave associated with the A(H1N1)2009 virus. (R.A.)