Hemolytic uremic syndrome (HUS), which is primarily associated with infections caused by Shiga toxin-producing Escherichia coli (STEC), is the leading cause of acute kidney failure in children under 3 years of age. In France, almost all cases of HUS are sporadic. In the absence of specific treatment for HUS and STEC infections, it is important to identify the risk factors for these infections in order to develop and implement appropriate prevention and control measures. A national case-control study was therefore conducted in 2000 and 2001 to identify risk factors for sporadic HUS in children under 15 years of age. One hundred and five cases of typical HUS (with prodromal diarrhea) identified by the network of pediatric nephrologists participating in HUS surveillance were compared with 196 controls matched for age, sex, and place of residence and selected by the case’s attending physician. For 61 cases, STEC infection was confirmed by testing for antibodies against the lipopolysaccharide of 26 STEC serogroups. Cases and controls were interviewed by telephone using a standardized questionnaire to collect sociodemographic and clinical information, as well as exposures (food, water, animal, environmental, and human) during the seven-day period preceding the onset of diarrhea in the case. Analyses were conducted on all HUS cases and on STEC-confirmed HUS cases. Analyses stratified by age (< or =1 year and > 1 year) and by season (May–September and October–April) were performed. In univariate analysis, the presence of diarrhea cases in the family (OR: 6.9; 95% CI: 3.1–17.3), the presence of diarrhea in the community frequented by the case (OR: 3.3; 95% CI: 1.3–8.9), consumption of undercooked ground beef (OR: 2.0; 95% CI: 1.1–3.8), and consumption of well water (OR: 5.9; 95% CI: 1.1–59.0) were statistically associated with the occurrence of typical HUS. The association with well water consumption was strongest during the May–September period (OR: 30.6; 95% CI: 1.2–767.4). During this same period, contact with cattle was also associated with the occurrence of STEC-confirmed HUS (OR: 14.2; 95% CI: 1.9–631.0). In multivariate analysis, the occurrence of typical HUS was independently associated with the consumption of undercooked ground beef (OR: 5.5; 95% CI: 1.4–21.8), the presence of diarrhea cases in the community (OR: 5.7; 95% CI: 1.0–32.5), and the presence of diarrhea cases within the family (OR: 3.7; 95% CI: 1.1–12.4). Our results indicate that the consumption of undercooked ground beef and person-to-person transmission within the family or community are the main risk factors for the occurrence of HUS associated with STEC infection in children under 15 years of age in France. To ensure the safety of ground beef consumption, particularly for the most vulnerable consumers (young children, the elderly, and the sick), a comprehensive assessment and management of this risk must be undertaken. Measures must be implemented at all levels, from production to consumption. Standard hygiene measures must be reiterated and implemented promptly in the event of diarrhea cases within a community or family. Young children should avoid contact with cattle or their manure, as well as the consumption of untreated water from wells or private springs. (R.A.)