Introduction - Epidemiological surveillance of communicable diseases in France, through the establishment of observatories or networks of physicians, enables large-scale study of the co-occurrence of certain epidemic episodes, such as influenza-like illnesses and childhood nasopharyngitis. Methods - We propose a method for estimating the time lag between the onset of an increase in the incidence of nasopharyngitis and that of influenza-like illnesses during the winter season. The data used were collected by the Hivern@le-KhiObs® observatory and the Sentinelles® network during the 2005–2006, 2006–2007, and 2007–2008. We estimated these time lags in metropolitan France, at both the national and regional levels. Results—For these three consecutive seasons, the increase in the incidence of nasopharyngitis preceded the onset of the influenza epidemic by a period ranging from 4 to 10 days. Conclusion - Monitoring trends in the incidence of nasopharyngitis could be considered a complementary indicator, confirming the imminent arrival of an influenza epidemic. (R.A.)