Members of an extended family reported gastrointestinal illness to the health department in February. Five members of the family had become ill after eating together on January 29 at a Minnesota restaurant. One of the cases was determined to be a secondary infection. Food histories of the family members indicated consumption of salad dressing at the January 29th meal was associated with illness. All four of the primary cases had salad dressing, and all five controls did not not have salad dressing. The etiology of the disease was determined to be Norovirus when a stool sample from the secondary case tested positive for this pathogen.