An outbreak of verotoxin-producing Escherichia coli O157 (VTEC O157) infections linked to an open farm occurred in eastern England in April and May 2007. This paper describes the investigation and highlights the importance of multidisciplinary collaboration for successful control of such outbreaks. There was a temporal cluster of 12 confirmed symptomatic cases of VTEC O157 and one asymptomatic carrier, from five families. The investigation revealed that four of these cases formed part of an outbreak involving two families who visited an open farm. The phenotypic and genotypic characteristics of the isolates from the two families and the putative farm animal contacts were indistinguishable, indicating that the animals were the source of the primary infections. No epidemiological link could be established between the remaining three families affected and the open farm or people having visited the farm. Control measures included improved hand washing facilities on the farm, information for visitors and staff, restricted access and suspended petting and feeding of animals, and thorough cleaning and disinfection of affected areas.