Among the population of the Foodborne Diseases Active Surveillance Network (FoodNet) surveillance areas ("FoodNet sites") in 1996, children under 12 months of age had the highest incidence of sporadic salmonellosis. We conducted a case-control study in 5 FoodNet sites to identify risk factors for sporadic infant salmonellosis. A case patient was a child under 12 months of age with a laboratory-confirmed, nontyphoidal serogroup B or D Salmonella infection. Twenty-two case patients were matched with 39 control subjects by age and either telephone exchange or vital record birth list. In a multivariate analysis, case patients were more likely to have a liquid diet containing no breast milk than a liquid diet containing only breast milk (matched odds ratio, 44.5; P=.04). Case-patients were more likely to reside in a household where a member had diarrhea (matched odds ratio, 13.2; P=.01). To decrease their infants' risk of salmonellosis, mothers should be encouraged to breast-feed their infants. Caretakers of infants should learn about salmonellosis, hand washing, and safe preparation of formula and solid food.