To determine risk factors for sporadic Salmonella serotype Heidelberg diarrheal disease, we conducted a population-based case-control study in 5 Foodborne Diseases Active Surveillance Network (FoodNet) surveillance areas in 1996-1997. Forty-four case patients and 83 control subjects matched by age and telephone exchange were asked about exposures during the 5-day period before onset of illness in the case patient. Risk factors for infection were evaluated using conditional logistic regression analysis. Eating eggs prepared outside the home remained the only significant risk factor for illness (matched odds ratio [MOR], 6.0; 95% confidence interval [CI], 1.2-29.6). The population-attributable fraction of S. Heidelberg infections associated with eating eggs prepared outside the home was 37%. Eliminating the risk associated with out-of-home egg consumption could substantially reduce the incidence of S. Heidelberg infections. Control measures to prevent S. Heidelberg infection should include advising consumers to avoid eating undercooked eggs and educating food handlers about proper egg handling and cooking.