Three cases of E. coli O157:H7 infections occurred in Minnesota residents. The cases were infected with a genetically indistinguishable strain of E. coli O157:H7. All three had eaten at locations of a Mexican style restaurant chain. An additional case, identified in a Washington state resident, also reported eating at one of the restaurant locations in Minnesota. Cases cases infected with the same strain of E. coli O157:H7 were identified in California and Colorado. These cases did not report eating at the restaurant chain. They had, however, had recently eaten beef. It is not clear whether these cases were linked to the cases reported by Minnesota. An inspection of the Minnesota restaurants suggested that cross contamination from steak could have occurred. However, the specific food vehicle and the source of contamination were never confirmed.