BACKGROUND: The burden of influenza and its clinical presentation are both poorly documented in French children. METHODS: To measure the prevalence of acute respiratory infections over two winters (2000 to 2001 and 2001 to 2002), we performed a prospective community survey of 0- to 15-year-olds (n = 11 500 and 40 000, respectively) through a network [Grippe et Infections Respiratoires Aigues Pediatriques (GIRAP)] of general practitioners and pediatricians. Influenza viruses were detected by antigen detection and culture from nasopharyngeal swabs. Data on the clinical presentation of children infected with influenza A/H1N1, A/H3N2 or B viruses were derived from standardized forms. RESULTS: The prevalences of symptomatic acute respiratory infections were 28% and 27% for 2000 to 2001 and 2001 to 2002, respectively. In the winter of 2000 to 2001, a mild outbreak of influenza A/H1N1 affected 5.4% of the study population. The attack rates of influenza A/H1N1 were highest in children 5 to 15 years of age. In the winter of 2001 to 2002, influenza activity remained at a subepidemic level (5.9%; A/H3N2, 60%; B, 40%). The incidence of influenza A/H3N2 infections was highest in 2- to 4-year-old children, whereas influenza B strains were most frequently detected in children 4 to 10 years of age. CONCLUSIONS: Despite subepidemic levels of influenza, the GIRAP network was able to detect influenza A or B viruses in 35 to 60% of the samples during the peak of influenza epidemic. The frequency of influenza virus excretion in children with mild clinical symptoms indicates that children are an important reservoir and source of transmission of this virus.