To assess the cost of varicella in young children in France, a prospective study was done in day care centers. Children (1263), who were 3 months to 3 years old and attending day care, were followed over a varicella season. For every child who developed varicella (n= 200), detailed information was obtained by use of parental questionnaires. Questions concerned medical care, days missed from work for parents, and the need for extra baby-sitting. On average, each sick child had one consultation with a physician and received three medications. In half of the families (52%), at least 1 parent had to miss work an average of 4.5 days to care for a sick child. Total costs to society were estimated to be US$352 per family, with medical costs accounting for 22% of the cost. The average eventual cost to parents was $89 per family, including $80 of non-medical costs. This study emphasizes the important socioeconomic impact of varicella in the day care setting in France.