To determine risk factors for the occurrence of sporadic Salmonella typhimurium infections among children in France, we conducted a matched case-control study. Cases were identified between 15 June and 30 September 1996. We interviewed 101 pairs of case patients and control subjects, matched for age and place of residence. The risk of illness was greater for children who ate undercooked ground beef than for those who did not (odds ratio [OR], 5.0; 95% confidence interval [CI], 1.9-13.1). Case patients were more likely than control subjects to have taken antibiotics during the month before onset of disease (OR, 2.2; 95% CI, 1.0-4.9). Case patients <5 years of age were more likely to have been in contact with a household member with diarrhea 3-10 days before onset (P=.05). Consumption of undercooked ground beef is a risk factor for the sporadic occurrence of S. typhimurium infection among children, and antibiotics may facilitate the occurrence of illness. The possibility of person-to-person transmission among young children needs to be considered.