Patrons of the Sunset House restaurant, Wyoming, developed Salmonella Heidelberg. The cases resided in six states. Epidemiological and laboratory analysis showed that canned mushrooms were the likely vehicle for transmission, although other food items may have been contaminated. The analysis showed that the mushrooms had not been contaminated during production as unopened cans of mushrooms showed no signs of contamination. Food handling practices at the restaurant likely contaminated the mushrooms.