Continuous surveillance of acute diarrhea in France has been conducted by Inserm's sentinel network of general practitioners (GP) since 1991. Similar GP-based studies have been performed in the Netherlands, Austria and the UK. The causes of most cases of acute diarrhea are unclear. In case-controlstudies designed to identify viruses in stools, 35 to 40% of cases and virtually none of the controls were positive for one of 4 major viruses (rotavirus, calicivirus, astrovirus and adenovirus). Thus, no viral cause was identified in more than 60% of patients with acute diarrhea. The causative role of viruses such as torovirus, picobirnavirus, picornavirus and enterovirus 22 has rarely been investigated. Further investigations are needed to identify other viral, bacterial fungal or parasitic causes of acute diarrhea. In France, on average, more than 3 million people (predominantly children) visit a GP for acute diarrhea each year. Most of these patients recover spontaneously within a few days, but the medical, social and economic costs of acute diarrhea are sufficiently high to justify a more aggressive public policy to prevent and control epidemics in Europe.