A public health monitoring program for the “Les Eurockéennes” rock music festival was established in July 2000 by CIRE Centre-Est, in collaboration with the Belfort DDASS and SAMU 90, and with support from the InVS. This was the 11th edition of an event held annually over three days near Belfort, attracting approximately 25,000 people daily, mainly teenagers and young adults. The goal of the surveillance system was the rapid detection of any abnormal situation that might require an investigation or urgent public health intervention. The report presents the implementation details of this surveillance and its results. In particular, it highlights the feedback provided to all partners involved in the initiative. The experience described here is useful for health services that wish to undertake this type of initiative. (R.A.).