Respiratory syncytial virus (RSV) bronchiolitis has become a major public health concern in France during the last decade. This winter epidemic mobilizes each year considerable means through the private ambulatory and public hospital nets. The epidemiology of RSV bronchiolitis remains difficult to characterize because of the lack of consensus for its definition. Several French studies are described here which suggest an increase in severity of the epidemics since 10 years in France. Peaks are more important each year and involve younger patients. This phenomenon does not concern other winter epidemics such as rotavirus gastroenteritis or influenza in infants. A policy of prevention of RSV bronchiolitis seams to be necessary in our country in the future.